Adds a thin read-only client for the actualbudget HTTP API
(`fire_planner/actualbudget.py`) and a `GET /spending/annual` endpoint
that returns trailing-N-month spending broken out by category group.
Default exclusions ("Investments and Savings", "Budget Reset") strip
out wealth transfers so the headline number reflects actual
consumption — for Viktor's data, ~£41k/yr instead of the raw £210k
total. Caller can pass `?exclude=...` to override.
Frontend uses the headline `total_gbp` to autofill the Annual spending
input (same pattern as nw_seed from networth), with a small
provenance line below the input showing the window + which groups
were excluded.
Auth: 3 new env vars (ACTUALBUDGET_API_URL/KEY/SYNC_ID) sourced from
Vault `secret/fire-planner` via the existing ExternalSecret —
infra/stacks/fire-planner applied separately. Backend silently keeps
the hardcoded default if the upstream is unreachable.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
