fix: type-check jq_collector under mypy strict (#52)

[tschm]

Closes #52

Acceptance criterion (verbatim): "uv run --frozen mypy passes with strict = true in [tool.mypy], and CI's Types step enforces it."

What changed

• collector/pyproject.toml: strict = true under [tool.mypy], and the "not --strict yet" comment updated. CI's Types step runs bare uv run --frozen mypy, which reads this table, so the workflow needs no change.
• The 32 errors strict mode surfaced, all annotation-only:
  • 26 × bare dict / list → dict[str, Any] / list[Any] in github.py, gitlab.py and repos.py. These hold forge JSON and raw YAML, whose shape the forge decides, so Any is the honest element type.
  • 4 × untyped defs in metrics.py: render, _health and FleetCollector.collect now return Iterator[Metric], and FleetCollector.__init__ takes a Store.
  • 2 × no-any-return in the forge clients' JSON getters: response.json() is now bound to an object before being returned, which is what the signature already promised.
• No behaviour change.

Gates (from collector/, as ci.yml runs them)

• uv run --frozen mypy: no issues in 11 files (strict)
• uv run --frozen ruff format / ruff check jq_collector tests: clean (the formatter rewrapped two long signatures)
• uv run --frozen python -m pytest --cov=jq_collector: 451 passed, 100%
• The same suite on --python 3.11: 451 passed, 100%

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