v0.3.0 - Autonomous PR Review Engine, AST Symbol Search, Capability Leases & Space UI

What's Changed in exist.io v0.3.0

🤖 Autonomous Agent Protocols & Engine (Milestone D)

• Automated PR Reviewer Engine (internal/agentreviewer): Automated diff analysis, AST inspection, credential and secret leak detection (AWS keys, GitHub tokens, Slack tokens, private keys, high-entropy tokens), test coverage threshold verification, automated quality scoring (0-100), check run & check suite integration, and telemetry streaming.
• Pure-Go AST Semantic Symbol Search (internal/symbolsearch): Go parser standard library AST extraction, TypeScript/JavaScript regex-based parser, and Python AST scanner. Exposes GET /v1/origin/repos/{ownerSlug}/{repoName}/symbols and new MCP tool search_symbols.
• Ephemeral Capability Leases (pkg/agentlease): HMAC-SHA256 cryptographically signed capability tokens with scoped branch prefix isolation (refs/heads/agent/*) and automatic TTL expiration. Mounted on POST /api/v1/agent/leases.
• Bounded Agent Activity Ring Buffer (internal/agentactivity): Thread-safe in-memory ring buffer streaming live agent tool executions and automated reviews to GET /api/v1/agent/activities.
• Expanded MCP Server (35 Tools): Added search_symbols to internal/mcp/tools.go with complete schema and handler.

🎨 Craft-First Space UI Elevating Enterprise Self-Hosting (Milestone E)

• PullRequestsView: Live PR fetching, authentic empty state with copyable Git branch/PR commands, live 'Run AI Agent Review' button with real-time analysis banner, and live 'Slide to Merge' execution.
• RepoOverview: Live tree fetching via getFiles(...), blob viewer with live contents, authentic empty state with copyable clone commands, and interactive Semantic Symbol Search input with debounced AST lookups and kind badges.
• AgentConsoleView: Live telemetry streaming from /api/v1/agent/activities, live JSON-RPC MCP tester, and interactive 'Capability Leases' generator drawer with 1-click token copying.
• API Client Upgrades: Enhanced web/src/lib/api.ts with agent activity streaming, lease minting, and AST symbol lookups.

📚 Documentation & Diátaxis Upgrades

• Added comprehensive MCP 35 tools catalog reference at site/docs/reference/mcp-tools.mdx.
• Updated Diátaxis docs site and built verified static assets with zero broken links.
• Updated ROADMAP.md and README.md reflecting completion of Phase 4 autonomous agent execution.