feat: extend latest_release filter options

[httpdss]

Summary

• add strip_v=False to remove exactly one leading lowercase v from the latest release tag while leaving tags without that prefix, uppercase V, and default-branch fallbacks unchanged
• add return_sha=False to return the commit SHA represented by the selected release tag, including lightweight and nested annotated tags
• document the new options, fallback/error behavior, and examples in both filter references

Backward compatibility and option interaction

Both parameters are appended optional booleans, so existing one-argument Python and Jinja calls preserve the current tag/default-branch/LATEST_RELEASE_ERROR behavior. When return_sha=True and strip_v=True are used together, SHA output takes precedence and strip_v is intentionally a no-op.

If latest-release selection fails, version mode retains the existing default-branch-name fallback; SHA mode resolves that branch head to a commit SHA. Once a release has been selected, tag-resolution failures return LATEST_RELEASE_ERROR rather than silently returning an unrelated branch revision.

Test coverage

Coverage includes:

• unchanged default behavior and disabled stripping
• lowercase v, repeated v, no-prefix, and uppercase V tags
• lightweight, annotated, and nested annotated tag resolution
• return_sha precedence when both options are enabled
• default-branch fallback in version and SHA modes
• malformed/missing refs, tag names, object types, object IDs, cycles, excessive nesting, and lookup failures
• cache isolation between calls/options

Validation

Passed:

• .venv/bin/pytest -q — 239 passed in 28.84s
• .venv/bin/pre-commit run --all-files — YAML, EOF, and trailing-whitespace hooks passed
• .venv/bin/mkdocs build — documentation built successfully in 5.95s (existing link warnings remain)
• .venv/bin/python -m compileall -q structkit tests — passed
• git diff --check origin/main...HEAD — passed
• live authenticated check against httpdss/structkit — default v3.2.1, stripped 3.2.1, SHA 892c7aa8d35d44bf7ffbe41ab4367a0933bd6b05

Additional repository-wide diagnostics expose existing baseline debt rather than regressions from this PR:

• mkdocs build --strict aborts on the same 9 pre-existing broken-link warnings on origin/main
• mypy structkit fails on both this branch and origin/main at unchanged structkit/commands/validate.py:99
• full black --check / flake8 are not currently clean on origin/main; focused changed-file comparison introduces no new failures (and tests/test_filters_more.py is now clean under both)