fix(cli): don't hang on ci explain with no --log in a terminal - #366

Problem

When --log is omitted, PatchRail reads the log from stdin — correct for the documented one-liner:

gh run view <run-id> --log-failed | patchrail ci explain

But a first-timer who just runs patchrail ci explain in a terminal — forgetting --log, with nothing piped in — hit a blocking sys.stdin.read() that waited forever with zero output. The program looked frozen or crashed, with no hint that it wanted input. Reproduced against the published 0.7.2 wheel (hangs >6s, no output, on a pty stdin).

Fix

_read_log now detects an interactive terminal on stdin (isatty()) with no --log and raises LogReadError with an actionable hint instead of blocking. explain, classify, pilot-pack and redact print it to stderr and exit 2 — the same clean contract as the other bad-input cases (missing file, directory, unreadable file, empty input):

patchrail ci explain: no log to read from stdin: pass --log <file>, or pipe a CI log in (e.g. `gh run view <run-id> --log-failed | patchrail ci explain`)

A real pipe or file redirect is untouched (its stdin is not a TTY), so the documented one-liner and every scripted use keep working exactly as before.

Tests

• +3 tests (explain/classify/redact): an interactive-TTY stdin with no --log exits 2, emits the hint, and leaks no traceback.
• Existing empty-stdin / missing-file / directory / unreadable tests unchanged and green (they model a pipe, isatty()→False).
• Full suite: 941 passed + 70 subtests (Python 3.12). ruff + format + mypy clean. Benchmark top-1 = 1.0 over 223 fixtures (no classifier/fixture change).