Tier 1 completion plan + proposals (B2a + B4 + B5)

[HumanBean17]

Summary

Adds the implementation plan and the two proposal documents for Tier 1
completion (B2a + B4 + B5) so an implementer can pick this up
end-to-end in Cursor without re-deriving the design.

This PR ships planning artifacts only — no production code changes.
The actual implementation lands in the five follow-on PRs the plan
specifies.

Files

• propose/TIER1-COMPLETION-PROPOSE.md — active proposal (B2a + B4 +
  B5) with brownfield route_overrides integration.
• propose/TIER1B-HTTP-ASYNC-EDGES-PROPOSE.md — skeleton for the
  follow-on B2b + B6 PR; locks the join-key contract with B2a so the
  two PRs cannot drift.
• plans/PLAN-TIER1-COMPLETION.md — implementation plan, split into
  five independent PRs.

PR breakdown the plan specifies

PR	Scope	Ontology bump
PR-A1	B2a schema + literal extractor (Route, EXPOSES, pass4_routes)	4 → 5
PR-A2	B2a SpEL / constant-ref resolution + read-only MCP tools	none
PR-A3	B2a brownfield (route_overrides, @CodebaseRoute, 5-layer resolver)	none
PR-B	B4 analyze_pr MCP tool	none
PR-C	B5 layered ignore patterns + diagnose_ignore MCP tool	none

PRs land in order A1 → A2 → A3 → B → C. PR-B and PR-C are
independently mergeable after A1 if priorities shift.

Out of scope

• B2b + B6 — imperative HTTP/async edges + cross-service matcher
  (separate proposal in this PR).
• Microservice-scoped CALLS — orthogonal small follow-up.
• B7 / B8 / B3 — separate proposals later.

Review checklist

• Proposal §3.1 join-key contract matches the Route schema in
  §4.3.
• PR-A3's brownfield design is a strict mirror of
  resolve_role_and_capabilities.
• PR-B's risk-score formula constants are flagged as v1 baselines.
• PR-C preserves behaviour for projects without
  .lancedb-mcp/ignore.