feat(git-pilot)!: redesign hook output and behavioral contract

[moukrea]

Summary

• Switch all hooks from systemMessage to additionalContext — hooks now provide facts that Claude reasons about, instead of user-facing warnings that never reached Claude's context
• Consolidate behavioral contract into CLAUDE.md — removed duplicated rules from workflow skill, added Rule 10 hook-response map that maps every hook context pattern to the correct Claude action
• Simplify all hook output — session-stop reduced from 50+ lines (full commit dumps) to max 5 concise fact lines; all hooks now emit single-line [git-pilot] prefixed facts
• Add 94 bats tests — full test coverage for session-start (24), session-stop (21), post-bash (15), post-write (14), and prompt-context (20)
• Bump version to 3.0.0 (breaking: output field rename, rule renumbering, skill simplification)
• Remove TECHNICAL-SPEC.md — implementation complete, spec no longer needed in repo

Breaking Changes

• Hook output field changed from systemMessage to additionalContext across session-start, session-stop, post-bash, post-write, and prompt-context hooks
• CLAUDE.md rules renumbered: old Rule 1 (hook compliance) removed and absorbed into new "How hooks work" intro + Rule 10
• git-pilot-workflow SKILL.md reduced to a lightweight CLAUDE.md reference (no longer contains behavioral rules)

Test plan

• 94 new bats tests all pass
• bash -n syntax check passes for all scripts
• No hook output contains anti-pattern strings (AskUserQuestion, You MUST, STOP and, Do not proceed, Execute this command immediately)
• All hooks use additionalContext exclusively (no systemMessage)
• 174/178 total tests pass (4 pre-existing failures unrelated to changes)