feat: AGENTS.md management, richer project UI, and improved cleanup

[Minitour]

Summary

This PR introduces first-class management of agent instruction files (AGENTS.md / CLAUDE.md), improves the web UI with richer project details, and fixes several gaps in the clean command.

Changes

Agent instruction file management

• Added a new agents section to the capabilities schema, allowing projects to declare a base file and a list of inline/remote/GitHub/GitLab snippets to inject into AGENTS.md (and CLAUDE.md when a Claude provider is active).
• Snippets are wrapped in HTML comment markers (<!-- capa:start:<id> --> … <!-- capa:end:<id> -->) for idempotent upsert/removal across installs.
• install now runs an agent-file install step after resolving capabilities (Step 3).
• clean now strips all capa-managed snippets from agent instruction files before unregistering the MCP server.
• The default capabilities template ships with an inline capa_tool_usage snippet and defaults toolExposure to on-demand.

Web UI improvements

• Project detail view now exposes richer server metadata: requiresOAuth, isConnected, displayName, cmd, and args.
• Tool entries now surface mcpServer/mcpTool (for MCP tools) and command/commandArgs (for command tools).
• New API endpoint GET /:projectId/servers/:serverId/tools to list tools available on a specific MCP server.

Improved cleanup

• cleanCommand now calls db.deleteProject(projectId) so project configuration and metadata are fully removed from the database on clean.

New types

• AgentFileConfig, AgentFileBase, AgentSnippet, AgentSnippetDef added to src/types/capabilities.ts.