feat: UI fixes + boocontext remainders — Memory project selector, agent event toasts, codecontext→boocontext left-overs

Fixes 3 remaining UI items from the component-wiring audit:
  - Memory page: project selector dropdown (Item 1)
  - Agent events: collision_warning + agent_message toasts via sonner (Item 2)
  - Reasoning delta already wired and working (Item 3)

Also picks up uncommitted boocontext rename changes from the subagent batch:
  - synthesisPipeline.ts tier tool names updated
  - tiers.ts STANDARD_TOOL_NAMES clears old codecontext tools
  - tool-utils.ts BUILT_IN_TOOLS updated
  - .env.example / README.md reference boocontext MCP
  - ROADMAP.md boocontext entry
  - codecontext/ dir + docs/codecontext-ts-plan.md removed (already gone from tree)

.codesight/middleware.md

@@ -5,7 +5,6 @@
 - authoring — `apps/coder/src/conductor/flows/authoring.ts`
 - turn-guard.test — `apps/coder/src/services/backends/__tests__/turn-guard.test.ts`
 - turn-guard — `apps/coder/src/services/backends/turn-guard.ts`
-- get_middleware — `apps/server/src/services/tools/codecontext/get_middleware.ts`
 - authoring — `conductor/src/flows/authoring.ts`
 - spec — `openspec/changes/add-behavioral-engine/specs/audit-middleware/spec.md`