feat: add AI-Agent and AI-Model trailers (GIT-73)

[TonyCasey]

Summary

• Wire AI-Agent and AI-Model trailers through the full remember flow (CLI, MCP, MemoryService)
• Update prepare-commit-msg hook to v2 with $GIT_MEM_MODEL detection and in-place upgrade from v1
• Env var detection: $GIT_MEM_AGENT / $CLAUDE_CODE for agent, $GIT_MEM_MODEL for model
• All new fields optional — zero breaking changes

Showcase

This commit itself demonstrates all 6 trailer types visible on GitHub:
AI-Decision, AI-Confidence, AI-Memory-Id, AI-Tags, AI-Agent, AI-Model

Plus a git note on refs/notes/mem with the full JSON memory.

Test plan

• 2 new MemoryService tests (agent/model trailers written, not written when absent)
• 4 new hook tests (AI-Model set, not set, both trailers, v1→v2 upgrade)
• All 372 tests pass
• Type-check and lint clean

Closes GIT-73

🤖 Generated with Claude Code

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[Copilot]

Pull request overview

This PR adds support for AI-Agent and AI-Model trailers throughout the git-mem codebase, enabling tracking of which AI agent and model created each memory. The implementation maintains backward compatibility by making both fields optional and provides consistent environment variable detection across all entry points.

Changes:

• Add AI-Agent and AI-Model trailer support to domain entities, service layer, CLI, MCP, and git hooks
• Upgrade prepare-commit-msg hook from v1 to v2 with automatic in-place upgrade logic
• Add comprehensive test coverage for new trailer functionality and hook upgrade behavior

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/domain/entities/ITrailer.ts	Adds MODEL: 'AI-Model' constant to AI_TRAILER_KEYS
src/domain/entities/IMemoryEntity.ts	Adds optional agent and model fields to ICreateMemoryOptions interface
src/application/services/MemoryService.ts	Updates buildTrailers to accept options parameter and conditionally write agent/model trailers
src/cli.ts	Adds --agent and --model CLI flags with environment variable defaults
src/commands/remember.ts	Implements agent/model resolution with fallback chain: explicit flag > GIT_MEM_AGENT/GIT_MEM_MODEL > CLAUDE_CODE
src/mcp/tools/remember.ts	Adds agent/model parameters to MCP remember tool with same resolution logic
src/hooks/prepare-commit-msg.ts	Upgrades hook to v2 with AI-Model support, adds fingerprint prefix detection for version upgrades, and implements in-place upgrade from v1
tests/unit/application/services/MemoryService.test.ts	Adds tests verifying agent/model trailers are written when provided and omitted when not provided
tests/unit/hooks/prepare-commit-msg.test.ts	Updates fingerprint expectations to v2, adds v1→v2 upgrade test, and adds tests for AI-Model trailer behavior with/without GIT_MEM_MODEL

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