Narrow developer session binding

[zccz14]

Summary

• Reduce AIM Developer to task/OpenCode session consistency: assign unbound tasks and recover missing session records only.
• Remove Developer-owned PR follow-up categorization, settlement prompting, dependency gating, and token-budget start gating.
• Replace legacy progression tests with focused behavior coverage and an architecture boundary guard.

Tests

• pnpm exec vitest run --config vitest.workspace.ts --project api modules/api/test/developer-boundary-architecture.test.ts
• pnpm exec vitest run --config vitest.workspace.ts --project api modules/api/test/developer.test.ts modules/api/test/developer-boundary-architecture.test.ts
• pnpm --filter ./modules/api run test:type
• pnpm --filter ./modules/api run test:lint
• pnpm --filter ./modules/contract run build:dist
• pnpm --filter ./modules/api run test:vitest