M11+N1: Wire ruleRole tiebreaker; prune dead code (closes #31, #32)

[curtyo18]

Summary

Bundles two cleanup issues into one commit:

M11 (#31) — Wire ruleRole into planDedupe (restoring spec §8.1's drive-role-priority tiebreaker) and remove @preact/signals (declared but never imported anywhere).

N1 (#32) — Remove prettier root devDep (in devDependencies but never called by any npm script), delete quarantineRoot function (not exported, not called), and remove export keyword from 5 unused exported types.

@hono/node-ws stays — its disposition is gated on F1 (#35).

Decisions made

• ruleRole: WIRE-UP chosen — planDedupe now loads rules from DB, finds the first matching rule for each duplicate group's copies, and passes matchedRule.destinationRole as ruleRole to the scorer. The scorer already handled this correctly in unit tests; the production call site had hardwired null. Also threads destinationTemplate while at it.
• @preact/signals: REMOVED — no current imports anywhere in packages/ui/src/, no adoption plan.
• @hono/node-ws: PRESERVED — F1 (F1: [Decision] processPriority OS integration and spec §11 WebSocket — implement or defer? #35) hasn't decided WebSocket/SSE browser delivery yet.
• prettier: REMOVED — declared in root devDeps but no npm script calls it.
• quarantineRoot: DELETED ENTIRELY — removing export triggered an ESLint no-unused-vars error because quarantine.ts itself never calls the function either. reconcile.ts uses its own local const quarantineRoot = join(...), not an import.
• @testing-library/preact: LEFT IN PLACE — imported in use-keyboard.test.tsx.
• jsdom: LEFT IN PLACE — configured as environment: 'jsdom' in vitest.config.ts and vite.config.ts.

Test plan

• ruleRole integration test: file with matching rule whose destinationRole is set → keeper is the copy on the role-matched drive, not the one with lower fileId
• npm install after dep removals — no errors
• knip re-run: @preact/signals, prettier, quarantineRoot, 5 unused type exports all gone from output
• Engine tests: 311 pass (310 baseline + 1 new ruleRole integration test)
• UI tests: 21 pass (baseline unchanged)
• npm run lint — clean
• npm run typecheck — clean

Out of scope

• @hono/node-ws removal (F1 / F1: [Decision] processPriority OS integration and spec §11 WebSocket — implement or defer? #35)
• createThrottleManagerRef (knip-flagged but not listed in N1: [Minor] Remove knip-confirmed dead devDeps and unused exports #32)
• New WebSocket/SSE delivery (F1)

Closes #31
Closes #32