feat(collab): agent/lender deal sharing — shareable links and PDF exports

[paruff]

Problem

Pros share deal analysis with agents (for offer submission) and lenders (for loan pre-approval). No shareable link or PDF export exists.

Acceptance Criteria

• Create `ShareLink` model: property, created_by, expires_at, access_token, permission_level (view/export)
• Generate secure random token (UUID4) for shareable URL: `/share//`
• Share page renders property analysis + underwriting KPIs + sensitivity + exit analysis
• Add "Export PDF" button on share page (generate PDF via WeasyPrint or ReportLab)
• PDF includes: property details, KPI table, sensitivity matrix, exit projections, financing comparison
• Configurable expiry: 24h, 7d, 30d, never
• Revoke access: owner can disable link at any time
• E2E test: create share link, access via incognito, verify PDF download
• Unit tests for token generation and expiry logic

Implementation Guide (for opencode/mimo v2.5)

1. Create `ShareLink` model in `core/models/sharing.py`
2. Create `share_view` in `core/views/init.py` with token lookup
3. Add PDF generation utility using WeasyPrint (server-side)
4. Create `templates/sharing/share.html` and `templates/sharing/pdf.html`
5. Add `share_link` creation endpoint (AJAX from property detail)
6. Add URL pattern `share/uuid:token/`
7. Tests in `tests/test_share_link.py`

Dependencies

• Requires: All analysis views (sensitivity, exit, financing) implemented
• Related: Issue feat(automation): saved searches with email/in-app notifications #374 (team sharing) — extends sharing to external non-users