feat(tools/fossil): Fossil VCS + integrated-tracker bridge (SQLite, Tcl/Tk)

[potiuk]

Add tools/fossil/ for Fossil — the distributed VCS with an integrated issue tracker, wiki, and forum in a single SQLite-backed file. Fossil is unusual in that it collapses the forge + tracker + VCS split the rest of our bridges assume: one tool covers what tools/github/ + a VCS shim cover separately. The bridge should expose both the version-control surface and the built-in tracker surface.

Capabilities to provide:

• VCS surface: fossil commit, fossil diff, fossil timeline (log), branch/checkout, file-at-version — via the shared VCS shim
• Tracker surface: ticket list/view/create/edit/comment via Fossil's ticket subsystem and JSON API
• Wiki/forum read (optional) for projects that keep docs/discussion there
• Write paths gated on explicit user confirmation in the calling skill

Why: Fossil is the home of SQLite (one of the most widely deployed pieces of software on earth), Tcl/Tk, and Fossil itself, plus a community of projects that deliberately chose an all-in-one self-hosted tool over the GitHub stack. Because tracker and VCS live together, a Fossil bridge lets the issue-* and dev-loop skill families work against a single endpoint.

Reference:

• Fossil: https://fossil-scm.org/
• JSON API: https://fossil-scm.org/home/doc/trunk/www/json-api/index.md
• Mirrors both the tools/github/ tracker shape and the VCS shim from the Mercurial bridge issue