feat(addie): brand-tools MCP support for distributed brand.json (#4527)

[bokelley]

Closes #4527.

Summary

Adds four Addie MCP tools that author and verify variant-5 Brand Canonical Documents and brand_refs[] pointer entries per the brand-protocol 3.1 spec (docs/brand-protocol/brand-json.mdx, ratified in #4505).

• publish_brand_canonical_document — generate a variant-5 Brand Canonical Document with the brand's identity fields and validate it against the brand.json schema before returning. Hosting is left to the operator.
• add_to_brand_refs — append a portfolio_entry pointer to a House Portfolio's brand_refs[], enforcing the Conformance section's cross-array uniqueness invariants (brand_id not in both brands[] and brand_refs[]; unique by domain and brand_id within brand_refs[]).
• check_mutual_assertion — fetch the leaf's canonical document and its claimed house's portfolio, follow House Redirects on the house side (3-hop cap per Conformance), and classify the relationship into mutual / leaf_only / house_only / standalone / unverifiable.
• notify_pending_verification — send the SHOULD-level notification email to the house's contact.email on leaf_only edges. Rate-limited per {leaf, house} pair at one notification per 24 hours via the new brand_assertion_notifications table. Gated behind BRAND_ASSERTION_EMAIL_ENABLED — defaults to log-only so the new send surface is opt-in.

Plumbing

• New module server/src/addie/mcp/brand-canonical-tools.ts. server/src/addie/mcp/brand-tools.ts re-exports BRAND_CANONICAL_TOOLS + createBrandCanonicalToolHandlers so existing import sites get the full surface in one file.
• Registered alongside the existing brand tools in three places: handler.ts (web Addie), bolt-app.ts (Slack Addie), and register-baseline-tools.ts (shared baseline).
• New migration 478_brand_assertion_notifications.sql — table keyed on (leaf_domain, house_domain) with last_notified_at and notification_count. Insert-or-update is a single statement so concurrent notifies can't both clear the cooldown.
• Schema validation: AJV against the source brand.json schema, with cross-file $refs (enums) preloaded synchronously at validator-compile time.

Trust-tier resolution detail

check_mutual_assertion enforces the spec's "standalone trumps third-party claim" rule by short-circuiting on house_domain absence — it never fetches the house when the leaf is silent. On the house side, it walks both house: \"<domain>\" and authoritative_location redirects up to 3 hops per Conformance.

Test plan

30 new unit tests in server/tests/unit/addie/brand-canonical-tools.test.ts. Coverage:

• publish_brand_canonical_document validates against the real source schema (sub-brand, standalone, invalid brand_id, empty names, extra filtering, domain normalization).
• add_to_brand_refs enforces all three uniqueness invariants from Conformance + variant-checks the house JSON + fetches when house_domain is supplied.
• check_mutual_assertion covers all five tiers + redirect-chain following + 3-hop limit + failure modes.
• notify_pending_verification rate-limits within 24h per {leaf, house} pair, lets a different leaf through, returns log_only when the feature flag is off (the default), and rejects invalid emails.
• Tool surface: all 4 tools registered, handler factory wires each, JSON contract round-trips correctly.

Results: 30 passed / 30 in this test file; 3497 passed across the full npm run test:server-unit run (one pre-existing flaky LLM-routing test unrelated to this change). Typecheck clean.