Make tools discoverable by descriptive group

[Gabriel-Darbord]

Summary

• add a static tool-catalog surface: discover-tools, inspect-tool, and call-tool
• add MCPToolExposurePolicy so each MCP server instance can configure which public tools are advertised statically
• keep non-static public tools discoverable and route discovery, inspection, and indirect calls through the same policy
• advertise common Pharo coding tools statically by default while keeping repository, history, removal, rewrite, UI, and other contextual tools discoverable
• keep broad operation tools intact for now; finer splits can follow separately
• document static/discoverable tool usage in user/AGENTS.md, with evaluate as an escape hatch

Performance

• move tool names to class-side metadata so registry and exposure checks do not instantiate every tool
• make tool icons shared and lazy through MCPToolIconSpec and MCPStructureIcon caches, avoiding eager PNG/ZLib work during MCP new
• make MCPTool inherit defaultName and defaultIcons from class-side metadata, removing duplicate concrete overrides
• add timeoutMilliseconds for run-tests and shorten the timeout fixture while preserving timeout/resume coverage
• gate run-tests Iceberg dirty-package refresh on image code-change announcements instead of refreshing unconditionally

Closes #23.

Verification

• image-side MCP-Tests concrete class selection: 503 tests passed in 22.324s, with the known Pharo 13 commit fallback skip
• image-side MCP-Spec-Tests: 38 tests passed in 0.093s
• image-side focused contract/edit/query/history/rewrite selection: 301 tests passed
• git diff --check

Current GitHub Actions failures on this branch did not reach project code; they failed during action archive download while GitHub Actions had an active codeload/action-download incident.