Add reviewed Content Inbox

[arumwu]

What

• add a local Content Inbox for inline text, URL references, and workspace-local files
• store content in SQLite with FTS5 search, SHA-256 deduplication, and content-addressed attachment copies
• expose four MCP tools and four matching CLI commands for ingest, search, review, and task promotion
• require explicit review before captured content can enter context packs or create an AgentRelay task
• make task promotion atomic and idempotent
• document the v0.5.0 workflow, trust boundary, security limitations, and deferred OCR/mobile/connector work
• refresh compatible MCP SDK and path-matching dependencies so the production audit is clean

Why

This keeps the ContentOS-style capture workflow inside AgentRelay instead of creating a second product. Agents can reuse reviewed source material and turn it into coordinated work while captured instructions remain untrusted by default.

Impact

• adds an additive content_items schema and a local .agentrelay/content/ attachment directory
• existing coordination, memory, Git, handoff, and tmux behavior remains unchanged
• URL ingestion stores a sanitized reference; it does not download the page
• raw attachment bytes are preserved, mode 0600, and are not secret-redacted or malware-scanned
• bumps the package and CLI version to 0.5.0; this PR does not publish to npm

Checks

• npm run check — 15 passed, 2 local tmux-dependent tests skipped
• MCP in-memory handshake — all 19 tools plus the review-gated content flow
• CLI smoke — ingest, blocked pre-review promotion, approve, promote, search, idempotent repeat
• npm pack --dry-run --json — 47 expected package files including CHANGELOG.md
• npm audit --omit=dev --audit-level=high — 0 vulnerabilities
• git diff --check origin/main...HEAD