Clickable file paths in the transcript open in the worktree #492

What the CLIs do

Grok Build: Cmd/Ctrl+click on paths the model prints (and on `images/1.jpg`) opens the file. Quoted paths, wrap-across-rows, and worktree sessions under `~/.grok/worktrees/` were all patched in 0.2.x. Claude/Kimi reveal a path from a tool card.

Solenta today

Assistant text is Markdown (`Markdown.tsx`) — only `http(s)` links are clickable. Tool cards and user bubbles are plain text. `shell.reveal` / `shell.openPath` already exist on the preload. Paths in a `Read` / `Edit` card or in "see `src/foo.ts:40`" are dead text.

Why it matters

Review is "open that file." Today you copy the path, switch to an editor, paste. The CLI already did the click. Same class as #469 (don't make me use a button for a path I can see).

Scope

1. In assistant Markdown and in tool-card headers/args, detect repo-relative and absolute paths (optional `:line` / `:line:col`).
2. Click (or Cmd-click) → `shell.openPath` or reveal in Finder; `:line` is a nice-to-have if the editor supports it.
3. Resolve relative paths against the thread worktree, not the main checkout.
4. Ignore URLs, npm package names, and paths that do not exist. No underline storm — underline on hover is enough.
5. Tests: relative file, missing file, `file:12`, http left alone.

Out of scope: a built-in editor (#162 is comments on diffs).

Round 25. Related: #186 (deep links), #155 (browser), #148 (diff view).