Add the Claude Code web SessionStart hook and bump the drift pin to v5

[tap]

What this changes

• Adds .claude/hooks/session-start.sh (canonical TapHouse copy) and .claude/settings.json to register it
• Bumps the TapHouse drift pin v4 → v5 in .github/workflows/style.yml

Why

PythonTap was one of three repos in the family without the canonical SessionStart hook. Fresh Claude Code web containers clone bare — no submodules, no pre-commit hook — so agent commits run unformatted and fail the clang-format gate on code a local clone would have fixed at commit time. The hook initializes source/min-api recursively, installs the pinned pre-commit hook, and warms its clang-format.

The pin bump is what makes the hook guarded rather than merely present: v4 does not carry .claude/hooks/session-start.sh, so the drift job's conditional guard would skip it silently. At v5 the guard becomes active.

Verification

Pre-flighted the drift gate: v4 and v5 carry byte-identical .clang-format, .clang-tidy, STYLE.md, .pre-commit-config.yaml and scripts/tidy.sh — the tags differ only by the addition of the hook — so the bump cannot change what the core comparisons expect.

Every file the v5 job will compare here already matches its canonical blob: .clang-format aedca32, .clang-tidy bb253e0, STYLE.md ebfcf54, .pre-commit-config.yaml b392057, scripts/tidy.sh 45fc009, and the new hook at b7c2a49 — which is identical at TapHouse v5, main, and in all nine consumers that already carry it.

Notes for the reviewer

.claude/settings.json is the canonical copy, created because none existed; it stays unguarded by design.

Two things from the same sweep that this PR does not address, both worth knowing:

1. This is the only repo in the family with no central C++20 policy. C++20 is set per-object on the external only, so the _test target stays at min-api's C++17 and the clang-tidy job is hardcoded to -std=c++17. The other Min-based packages force C++20 centrally in the root CMakeLists.txt.
2. package-info.json.in and the README badges still point at tap/Python-Max — the pre-rename identity.

Credit where due: this repo is also the only one in the family running ctest on both macOS and Windows, and the only one with the otool -L | grep @rpath/libpython check.

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