[beadboard] Add quality filters for acceptance criteria and description length

## Context

The left-panel task list surfaces every bead regardless of whether the task
has been specified thoroughly enough for an agent to pick it up. Tasks with
empty `acceptance_criteria` or very short descriptions are low-signal noise
that muddles the navigation spine — especially now that we plan to dispatch
tasks to Claude agents (which need concrete instructions to succeed).

Epics are deliberately exempt: their role is grouping, not execution, so
requiring acceptance criteria / long descriptions on epics would hide the
entire backbone of the navigation.

## This change

- Plumbs `acceptance_criteria` end-to-end: adds the optional field on
  `BeadIssue`, and reads it both from `.beads/issues.jsonl` (parser) and
  Dolt SQL (`read-issues-dolt.ts` row shape + normalizer).
- Extends `LeftPanelFilters` with `hideNoAcceptance` and
  `hideShortDescription` (both default `true`) in the source-of-truth
  `hooks/use-url-state.ts` and in the re-exported shadow type on
  `components/shared/left-panel.tsx`.
- Updates `isTaskMatch` in both `left-panel.tsx` and `left-panel-new.tsx`
  to skip non-epic tasks lacking acceptance criteria or with a description
  shorter than `SHORT_DESCRIPTION_MIN_LENGTH` (200 chars). Epics bypass
  both filters via the `issue_type === 'epic'` guard.
- Exposes `isTaskMatch` from `left-panel.tsx` so the filter tests can
  assert behavior directly (previously only `shouldHideEpicEntry` was
  exported).
- Adds two checkboxes under the existing "Hide Closed" button in both
  left-panel variants (legacy `left-panel.tsx` and the one unified-shell
  currently wires up — `left-panel-new.tsx`).
- Seeds both new filter flags as `true` in the `UnifiedShell` default
  state so fresh sessions see the high-signal view without toggling.

## What is NOT in this change

- No mutation of `bd` / CLI behavior. Filters are purely UI-level.
- No localStorage persistence for the two new flags — existing
  `hideClosed` is also React-only, so parity is preserved. If/when we
  persist any of these, all three move together.
- No change to the `metadata.acceptance` path used by `kanban.ts`'s
  `hasQualitySignal` — that's a separate signal with its own callers.

## Test Plan

### Automated

Tests run from `/home/wizard/code/beadboard`:

```
$ node --import tsx --test tests/components/shared/left-panel-filtering.test.ts
# tests 15
# pass 15
# fail 0
# duration_ms 604
```

All 15 filter cases pass: 6 pre-existing `shouldHideEpicEntry` cases plus
9 new `isTaskMatch` cases covering acceptance-criteria-empty hides,
acceptance-criteria-disabled shows, epic exemption, 199/200-char
description boundary, null description, and short-description flag
disabled.

Related suites still green:

```
$ node --import tsx --test tests/components/shared/left-panel.test.tsx \
    tests/components/shared/unified-shell-hide-closed-contract.test.ts
# tests 7 pass 7 fail 0
```

Pre-existing failures in `tests/hooks/url-state-integration.test.ts`
(`view=activity` cases) and one pre-existing typecheck error in
`left-panel.tsx` thread prop are unrelated — both reproduce on `main`
before this change.

### Manual Verification

1. `npm install`
2. `npm run dev`
3. Open `http://localhost:3000` with bd project loaded.
4. Expected: two new checkboxes appear under "Hide Closed" in the left
   sidebar — "Hide tasks without acceptance criteria" and
   "Hide tasks with short description (<200 chars)". Both checked by
   default.
5. Toggle each off. Expected: additional beads appear in epic expansions
   (tasks that were previously hidden because they lack quality signal).
6. Confirm epics remain visible regardless of the checkbox state.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/components/shared/left-panel-filtering.test.ts

@@ -1,7 +1,8 @@
 import test from 'node:test';
 import assert from 'node:assert/strict';
 
-import { shouldHideEpicEntry, type LeftPanelFilters } from '../../../src/components/shared/left-panel';
+import { isTaskMatch, shouldHideEpicEntry, type LeftPanelFilters } from '../../../src/components/shared/left-panel';
+import type { BeadIssue } from '../../../src/lib/types';
 
 const defaultFilters: LeftPanelFilters = {
   query: '',
@@ -9,8 +10,38 @@ const defaultFilters: LeftPanelFilters = {
   priority: 'all',
   preset: 'all',
   hideClosed: true,
+  hideNoAcceptance: true,
+  hideShortDescription: true,
 };
 
+function makeIssue(overrides: Partial<BeadIssue> = {}): BeadIssue {
+  return {
+    id: 'test-1',
+    title: 'Test issue',
+    description: 'x'.repeat(400),
+    status: 'open',
+    priority: 2,
+    issue_type: 'task',
+    assignee: null,
+    templateId: null,
+    owner: null,
+    labels: [],
+    dependencies: [],
+    created_at: '2026-01-01T00:00:00Z',
+    updated_at: '2026-01-01T00:00:00Z',
+    closed_at: null,
+    close_reason: null,
+    closed_by_session: null,
+    created_by: null,
+    due_at: null,
+    estimated_minutes: null,
+    external_ref: null,
+    acceptance_criteria: 'Some acceptance criteria text',
+    metadata: {},
+    ...overrides,
+  };
+}
+
 test('does not hide epics with no children when hideClosed is the only active toggle', () => {
   const hidden = shouldHideEpicEntry({
     epicStatus: 'open',
@@ -82,3 +113,50 @@ test('hides closed selected epic when hideClosed is enabled', () => {
 
   assert.equal(hidden, true);
 });
+
+test('hideNoAcceptance=true hides task with empty acceptance_criteria', () => {
+  const task = makeIssue({ acceptance_criteria: '' });
+  assert.equal(isTaskMatch(task, defaultFilters), false);
+});
+
+test('hideNoAcceptance=true hides task with whitespace-only acceptance_criteria', () => {
+  const task = makeIssue({ acceptance_criteria: '   \n\t  ' });
+  assert.equal(isTaskMatch(task, defaultFilters), false);
+});
+
+test('hideNoAcceptance=false shows task with empty acceptance_criteria', () => {
+  const task = makeIssue({ acceptance_criteria: null });
+  const filters = { ...defaultFilters, hideNoAcceptance: false };
+  assert.equal(isTaskMatch(task, filters), true);
+});
+
+test('hideNoAcceptance=true keeps epic visible regardless of acceptance_criteria', () => {
+  const epic = makeIssue({ issue_type: 'epic', acceptance_criteria: null });
+  assert.equal(isTaskMatch(epic, defaultFilters), true);
+});
+
+test('hideShortDescription=true hides task with 199-character description', () => {
+  const task = makeIssue({ description: 'x'.repeat(199) });
+  assert.equal(isTaskMatch(task, defaultFilters), false);
+});
+
+test('hideShortDescription=true shows task with 200-character description', () => {
+  const task = makeIssue({ description: 'x'.repeat(200) });
+  assert.equal(isTaskMatch(task, defaultFilters), true);
+});
+
+test('hideShortDescription=false shows task with short description', () => {
+  const task = makeIssue({ description: 'short' });
+  const filters = { ...defaultFilters, hideShortDescription: false, hideNoAcceptance: false };
+  assert.equal(isTaskMatch(task, filters), true);
+});
+
+test('hideShortDescription=true keeps epic visible regardless of description length', () => {
+  const epic = makeIssue({ issue_type: 'epic', description: 'short' });
+  assert.equal(isTaskMatch(epic, defaultFilters), true);
+});
+
+test('hideShortDescription treats null description as length 0', () => {
+  const task = makeIssue({ description: null });
+  assert.equal(isTaskMatch(task, defaultFilters), false);
+});