feat(plugin): add session title rename tool

[VooDisss]

Fixes #306

Summary

This change adds a dedicated plugin tool for renaming the active session title and wires it through the existing CodeNomad plugin bridge to the correct OpenCode workspace instance.

The goal is to let the assistant perform the same session title rename operation that already exists in the UI, without introducing a separate metadata store or bundling in the still-unsettled description feature.

Why

Users can already rename sessions manually in the UI, but there was no supported end-to-end conversational path for the assistant to do the same thing.

That mismatch meant the assistant could acknowledge a rename request without having a repo-native implementation path to update the actual session title. This PR closes that gap with the smallest correct change and keeps the scope intentionally limited to title renaming only.

What Changed

1. Added a new rename_session plugin tool in packages/opencode-config/plugin/lib/session.ts.
2. Registered the session tool set in packages/opencode-config/plugin/codenomad.ts.
3. Added a plugin server endpoint in packages/server/src/server/routes/plugin.ts that proxies title updates to the workspace OpenCode instance.
4. Forwarded the current tool execution directory so the rename follows the existing worktree-aware session targeting behavior.
5. Corrected the proxy implementation to use PATCH, matching the real OpenCode SDK session.update contract.

Scope Boundaries

Included:

• Session title rename tool
• Plugin registration
• Server bridge for title updates
• Worktree-aware forwarding via directory context

Not included:

• Description persistence
• Description rendering in the UI
• Session tooltip changes
• Any broader session metadata model changes

Technical Notes

The OpenCode SDK contract for session updates is not POST; it is PATCH /session/{sessionID} with a body containing the updatable fields such as title.

That detail matters because the first implementation path could appear successful while failing to apply the rename if the bridge used the wrong HTTP method. The final implementation aligns the server proxy with the generated SDK contract so the rename is applied by the actual OpenCode session update endpoint.

Files Changed

• packages/opencode-config/plugin/codenomad.ts
• packages/opencode-config/plugin/lib/session.ts
• packages/server/src/server/routes/plugin.ts

Verification

Performed:

1. Verified the generated OpenCode SDK contract for session.update.
2. Confirmed the plugin can call the new bridge endpoint.
3. Confirmed the feature works after switching the proxied request from POST to PATCH.
4. Rebuilt packages/server successfully.

Build note:

• The server build passes.
• The build still emits existing UI/Vite warnings unrelated to this change.

Risks and Follow-up

1. Description handling remains intentionally postponed and should be handled as a separate follow-up once the storage and UX direction is settled.
2. If future session metadata tools are added, they should continue to reuse the same plugin bridge pattern instead of creating parallel storage behavior.