Fix master defects + supersede broken 1.0.7

[onlykey]

Summary

Fixes the defects identified in a fresh code review of master (the two commits that landed since the 2023 idle period). All 8 commits are scoped to one concern each. Patch built from a local clone, verified with py_compile + pyflakes (no new warnings vs. master), and the new slot parser was unit-tested on six representative inputs before pushing.

Critical fixes

• libagent/device/onlykey.py — get_sk_dk() no longer crashes with TypeError when both AGENTHOMEDIR and GNUPGHOME are unset. Falls back to the default slot with a debug log instead of passing None into os.path.join.
• libagent/device/onlykey.py — slot parser rewritten. The previous hand-counted character-offset parser would silently fall back to slot 132 on any whitespace/quoting/ordering drift in run-agent.sh — a correctness-of-cryptographic-identity issue in a hardware-signing path. Replaced with two re.compiled patterns + a small _parse_slot_value() helper. Same semantics for the well-formed inputs the old code handled (ECCn, ECCnn, RSAn, plain n), and unrecognized values now log a warning instead of silently producing a wrong slot.
• libagent/device/onlykey.py — NotFoundError format string fixed. connect() was raising interface.NotFoundError('{} not connected: "{}"') with the literal braces unfilled. Now formats device name and the underlying exception.

Hygiene / packaging

• setup.py — version 1.0.7 → 1.0.8 so the broken 1.0.7 sdist from PR Replaced pkg_resources #12 (which removed import pkg_resources but left pkg_resources.require(...) behind in three modules) is unambiguously superseded. PR Complete pkg_resources removal for Python 3.14 + dependency/CI cleanup #15 fixed the regression on master but kept the same version string; bumping resolves that ambiguity for installers.
• libagent/util.py — new format_versions(agent_package) helper that catches metadata.PackageNotFoundError and degrades to (version unknown) for source-checkout development.
• libagent/age/__init__.py, libagent/gpg/__init__.py, libagent/ssh/__init__.py — three duplicated metadata.distribution(...) blocks now call util.format_versions(); stray from importlib import metadata imports removed.
• libagent/gpg/__init__.py — two stale commented-out log.warning(...) blocks dropped.
• tox.ini — isort>=5 → isort>=5,<7 to prevent a future isort major from breaking the build.
• .github/workflows/ci.yml — actions/checkout@v4 and actions/setup-python@v5 pinned to commit SHAs (v4.3.1 / v5.6.0) so a compromised tag can't push code into a hardware-key project's CI.

Deliberately not in this PR

• setup.py platforms=['POSIX'] and the POSIX classifier — left alone. gpg/__init__.py still shells out to mkdir -p / chmod and generates a #!/bin/sh run-agent script, so claiming OS-independent on master would advertise support that doesn't actually work. Belongs with the Windows-native runtime work in Sync with upstream trezor-agent; preserve OnlyKey features + add native Windows #16, not as housekeeping.
• The os.environ['AGENTHOMEDIR'] coupling between gpg/__init__.py and device/onlykey.py — that's an architectural change worth doing separately.
• The raw SSH-RSA byte-concat in device/onlykey.py:pubkey() — pure refactor, not a defect.

Verification

• python3 -m py_compile on every touched file — passes.
• python3 -m pyflakes — no new warnings versus master (only line numbers shifted for pre-existing unused imports the recent lint cleanup didn't tackle).
• Standalone smoke test of the new slot-parsing logic against ECC1, ECC16, RSA2, plain 132, multi-line shell-continuation form, and missing-flags — all return the expected slot.