Tasks: derive the CLI version from package metadata

Phase 3 of 3 (bugfix → design → tasks).

• [x] T1 — Derive __version__ from metadata. In cli/the_loop/__init__.py, replace the hardcoded "0.1.0" with importlib.metadata.version("the-loopy-one"), falling back to a 0.0.0+unknown sentinel on PackageNotFoundError. (AC 1–3)
• [x] T2 — De-duplicate the webhook version. In cli/the_loop/webhook/server.py, import __version__ and build server_version from it instead of the hardcoded "the-loop-gh-webhook/0.1.0". (AC 4)
• [x] T3 — Regression tests. In cli/tests/test_cli.py, assert __version__ matches importlib.metadata.version("the-loopy-one"), is not "0.1.0", and that --version prints the-loop <version>. (AC 1–2)
• [x] T4 — Capability doc. Record the derived-version behaviour and the fix in docs/capabilities/cli.md (current behaviour + history row).
• [x] T5 — Gates. ruff check / ruff format --check, pyright, and pytest all green.