Make demo actions reliable under retries and failures

[SaarthurR]

Why

Demo Server Actions could fail before dispatch when action modules re-exported non-function state, and retrying request acceptance could leave a fulfilled request without its chat recovery path. Report and cancellation layers also needed settled-state cleanup so failed or pending actions do not strand controls.

What this changes

• Keeps file-level Server Action modules limited to async runtime exports and adds a repository-wide TypeScript contract.
• Makes ride-request acceptance idempotent for the winning driver while emitting exactly one notification.
• Uses the privacy-safe public ride-detail RPC and preserves desktop/mobile loading behavior.
• Prevents report-layer dismissal during submission and resets report/cancellation feedback consistently.

Verification

• npm test — 395 passed, 0 failed
• npm run lint — passed
• npx tsc --noEmit — passed
• npm run build — passed on Next.js 16.2.9
• focused polish/action contracts — 17 passed, 0 failed
• live Supabase acceptance checks confirmed first accept true, same-driver retry true, other-driver false, one correctly attributed notification, and chat recovery

Migration note

The included migrations 20260713175559_public_ride_detail.sql and 20260713190208_accept_ride_request_idempotent_retry.sql are already applied to the linked Supabase project. Two earlier location-privacy migrations in the working tree are intentionally excluded from this PR because they predate and are outside this change set.

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