fix(agents): alias Pi tool names that collide with its built-ins

[vitaliyslion]

Summary

Pi has no native MCP support — extensions register tools into a flat, unprefixed registry, and Pi lets a same-named registration silently override a built-in (read, bash, edit, write, grep, find, ls). Gortex's default facade-v1 surface includes edit and read, so the Pi bridge was overriding those two built-ins with a generic relay that doesn't match Pi's expected result shape — breaking the built-in's own rendering (edited filename showed as "...") and any extension hooked to the built-in shape (e.g. a lint-on-edit plugin expecting the native edit tool).

Changes

• Alias only the tools that actually collide with Pi's reserved built-in names (gortex_edit, gortex_read today) instead of prefixing every Gortex tool, since a blanket prefix has previously confused the model — Gortex's own guidance and tool descriptions reference bare names elsewhere.
• safeRegister now registers under the alias name and returns the name actually used; registerOneTool dedupes against the aliased name.
• Session orientation now appends a short Pi-local note listing any renamed tools this session, so the model knows to translate bare names it sees in Gortex's guidance into the aliased ones.
• This logic lives entirely in the Pi extension (internal/agents/pi/extension/index.ts) — no server-side/shared code changed, since the collision is specific to Pi's flat tool registry.
• Regenerated the golden extension snapshot (cmd/gortex/testdata/agent-render/pi.txt).

Testing

• All tests pass (go test -race ./...)
• New tests added for new functionality — covered by the existing golden-snapshot test (TestAgentsRenderGolden) for the embedded extension source; no separate unit test added
• Benchmarks run if performance-relevant — not applicable

Checklist

• Code follows existing patterns in the codebase
• No unnecessary abstractions added
• Language extractor includes Meta["methods"] for interfaces (if applicable) — not applicable
• Methods have EdgeMemberOf edges to their containing type (if applicable) — not applicable