feat: client proposal management dashboard (#213)

[Cmitchelle7]

Closes #213

Summary

Proposal management dashboard for clients to review, filter, and manage freelancer proposals.

Endpoints

• GET /api/proposals?projectId=... — list (client sees all for the project, freelancer sees their own)
• PATCH /api/proposals/:id — accept/reject (client only, 403 for others)

UI

• app/dashboard/proposals/[projectId]/page.tsx — dashboard page
• components/proposals/* — filters bar, card, confirm dialog, status badge, skeleton, empty state

Data

• lib/db/migrations/010_proposals.sql — creates proposals and proposal_audit_logs
• lib/proposals/service.ts — Neon-backed list/update with audit trail

Acceptance criteria

• List proposals
• Freelancer preview (name, skills, rating, completed jobs)
• Proposed budget with currency formatting
• Estimated completion time
• Accept/reject with confirmation dialog
• Proposal status (Pending / Accepted / Rejected / Updated)
• Filter by status
• Role-based UI (clients manage, freelancers read-only)
• Empty state
• Loading state (skeleton)
• Responsive (mobile + desktop)

Additional

• Sort by budget / delivery time / rating / recent
• Audit trail (proposal_audit_logs on every accept/reject)

Notes

• Dynamic ORDER BY uses Neon tagged-template fragments + a whitelisted column list (no .unsafe(), no injection).
• The existing lib/db.ts sql proxy fails under Turbopack with "sql is not a function"; lib/proposals/db.ts provides a scoped direct neon() instance for this feature. Fixing the shared proxy is out of scope for this issue.

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