[ci skip] Move Terraform modules into stack directories

Move all 88 service modules (66 individual + 22 platform) from
modules/kubernetes/<service>/ into their corresponding stack directories:

- Service stacks: stacks/<service>/module/
- Platform stack: stacks/platform/modules/<service>/

This collocates module source code with its Terragrunt definition.
Only shared utility modules remain in modules/kubernetes/:
ingress_factory, setup_tls_secret, dockerhub_secret, oauth-proxy.

All cross-references to shared modules updated to use correct
relative paths. Verified with terragrunt run --all -- plan:
0 adds, 0 destroys across all 68 stacks.

stacks/f1-stream/module/files/internal/models/models.go

@@ -0,0 +1,53 @@
+package models
+
+import (
+	"time"
+
+	"github.com/go-webauthn/webauthn/webauthn"
+)
+
+type User struct {
+	ID          string                `json:"id"`
+	Username    string                `json:"username"`
+	IsAdmin     bool                  `json:"is_admin"`
+	Credentials []webauthn.Credential `json:"credentials"`
+	CreatedAt   time.Time             `json:"created_at"`
+}
+
+// WebAuthn interface implementation
+func (u *User) WebAuthnID() []byte                         { return []byte(u.ID) }
+func (u *User) WebAuthnName() string                       { return u.Username }
+func (u *User) WebAuthnDisplayName() string                { return u.Username }
+func (u *User) WebAuthnCredentials() []webauthn.Credential { return u.Credentials }
+
+type Stream struct {
+	ID          string    `json:"id"`
+	URL         string    `json:"url"`
+	Title       string    `json:"title"`
+	SubmittedBy string    `json:"submitted_by"`
+	Published   bool      `json:"published"`
+	Source      string    `json:"source"`
+	CreatedAt   time.Time `json:"created_at"`
+}
+
+type ScrapedLink struct {
+	ID        string    `json:"id"`
+	URL       string    `json:"url"`
+	Title     string    `json:"title"`
+	Source    string    `json:"source"`
+	ScrapedAt time.Time `json:"scraped_at"`
+	Stale     bool      `json:"stale"`
+}
+
+type Session struct {
+	Token     string    `json:"token"`
+	UserID    string    `json:"user_id"`
+	ExpiresAt time.Time `json:"expires_at"`
+}
+
+type HealthState struct {
+	URL                 string    `json:"url"`
+	ConsecutiveFailures int       `json:"consecutive_failures"`
+	LastCheckTime       time.Time `json:"last_check_time"`
+	Healthy             bool      `json:"healthy"`
+}