Fix YAML escape miscompile and harden init/doctor flow

[christopherarter]

Summary

Addresses review feedback from a real bully-init session. Priority-ordered:

P0 — silent miscompile

• _parse_scalar now processes YAML double-quoted escapes (\\, \", \n, \t, \r, \/, \0) and single-quoted '' → '. Previously it stripped outer quotes only, so "\\." stayed as two literal backslashes. Every shipped examples/rules/*.yml regex (react-ts, rust-cli, nextjs, django, go, fastapi, rails) exited 0 on grep's parentheses not balanced error — silent pass.
• filter_rules handles ** recursively via a new _scope_matches helper. PurePath.match only gained recursive ** in Python 3.13, so apps/**/*.ts was broken on 3.10–3.12 despite docs promising otherwise.
• Doctor's Python check actually compares sys.version_info against 3.10 instead of printing [OK] unconditionally.

P1 — UX

• Doctor accepts skills + the evaluator agent at either the legacy path or ~/.claude/plugins/cache/*/bully/*/{skills,agents}/... — plugin-installed users no longer get five bogus [FAIL] lines.
• bully shell wrapper at repo root so plugin users can alias/symlink without pip install.
• bully-init Step 6 now runs trust → doctor → telemetry dir + .gitignore (gated on Step 3 answer) → per-rule smoke tests before handing off. Would have caught the parser bug above at author time.

P2

• bully validate --execute-dry-run runs each script rule against /dev/null to surface shell/regex syntax errors at config time.
• docs/rule-authoring.md documents YAML escapes, ** compatibility, --explain, and --execute-dry-run.

Test plan

• Full suite: 297 passing (+5 new tests — escape handling, recursive globs, version gating, plugin paths, dry-run execution)
• Manual: ./bully doctor under system Python 3.9 → [FAIL] Python 3.9 < 3.10 -- upgrade required
• Manual: ./bully doctor under venv Python 3.12 → all [OK] including plugin-path skill detection ((plugin install) annotation)
• Manual: ./bully validate --execute-dry-run on repo's own .bully.yml → 6 script rules clean, ast/semantic rules correctly skipped
• Verified: shipped examples/rules/react-ts.yml console.log pattern now parses to console\.log\( instead of console\\.log\\( and grep runs cleanly
• Reviewer smoke-test on a fresh plugin install (no pip install) — confirm bully doctor passes without legacy-path files present