feat: queue and reconcile offline service mutations

[woahwhattheheck]

Closes #630.

Summary

Adds a persistent offline mutation queue for services-dashboard create and price-update actions, then reconciles queued work when connectivity returns.

• queue service mutations in browser storage while offline or after a network/timeout failure;
• preserve persisted enqueue order during replay;
• single-flight concurrent flushes and coalesce adjacent duplicate clicks without collapsing intentional A → B → A edits;
• preflight server state before replay and verify server state after a write so retries do not blindly double-apply;
• surface 409/412 and state drift as explicit conflicts;
• keep 429, 5xx, network failures, and unverified post-write readback pending/retryable rather than falsely classifying them as conflicts;
• extend the existing offline banner with queue/sync/conflict status plus retry/discard controls;
• integrate both service creation and price editing with the queue;
• retain deleted offline update targets (404 preflight) as discardable server conflicts rather than endlessly pending retries;
• return stable typed messages for immediate mutation errors without exposing raw server error text.

Acceptance coverage

• offline mutation → persisted queue + queued UI state;
• reconnect → FIFO flush;
• reload-shaped storage read → queue survives;
• duplicate flush → single-flight / no duplicate write;
• server conflict → surfaced and retained for operator resolution;
• unit coverage for queue ordering, idempotent recovery, conflicts, and retryable failures;
• integration coverage for NewServicePage offline persistence.

Validation boundary

The current carrier has 13 commits and 8 changed files at head e9831bf57b35d0f1800d9e91376a89d681075eff. Source includes focused regressions for uncertain create preflight, deleted update targets, and safe typed mutation errors. An earlier focused receipt records seven queue cases passing; that is historical evidence, not execution of the later regressions. No fresh full lint, test, build, or current-head CI-green claim is made here.

No CRDT/background-service-worker expansion is included.

Hosted CI status

Historical workflow run 37506558258 failed during npm ci before lint/tests/build because of sponsor package/lock drift. This carrier does not modify package.json or package-lock.json; the separate dependency repair is PR #644. Its green run is not validation of this queue carrier. Current-head hosted checks remain authoritative.

[woahwhattheheck]

/claim #630

Existing issue-level claim: #630 (comment)

I, @woahwhattheheck, affirmatively claim original-contributor credit for PR #642 and request evaluation for any applicable GrantFox OSS / Official Campaign (FWC26) reward and payment if accepted. Current carrier head: e9831bf57b35d0f1800d9e91376a89d681075eff.