Refactor: Commit message build, simplify Issue-ID handling

[ModeSevenIndustrialSolutions]

Major Changes:

1. Centralized Commit Message Building

   • Created _build_commit_message_with_trailers() as single source of truth
   • Consolidated duplicate trailer logic from 3 separate code paths
   • Now handles Issue-ID, Signed-off-by, Change-ID, and GitHub metadata
   • Ensures consistent trailer ordering across all modes (squash, single, PR-as-commit)
   • Reduced code by ~200 lines, improved maintainability

2. Simplified Issue-ID Lookup

   • Removed ISSUE_ID_LOOKUP input (auto-enabled when JSON provided)
   • Moved JSON lookup logic from GitHub Actions to Python CLI
   • Removed dependency on external json-key-value-lookup-action
   • Added JSON validation with clear warning messages
   • Simplified action.yaml by ~50 lines (removed 3 workflow steps)

3. Enhanced User Experience

   • Added Issue-ID to configuration table output
   • Added console feedback: "✅ Added Issue-ID {value} to commit message"
   • Added warning output: "⚠️ Warning: Issue-ID JSON was not valid"
   • Issue-ID now added in ALL modes (squash, single commits, USE_PR_AS_COMMIT)

4. Code Quality

   • Fixed all pre-commit linting errors
   • Added issue_id_lookup_json parameter to all test fixtures
   • All tests passing with 67.2% coverage
   • Updated README documentation

[Copilot]

Pull Request Overview

This PR moves Issue-ID lookup logic from GitHub Actions workflow steps to Python code, simplifying the action and centralizing trailer management. The change eliminates the external json-key-value-lookup-action dependency and consolidates commit message trailer handling into a single function.

Key changes:

• Migrated Issue-ID JSON lookup from bash steps to Python (_resolve_issue_id_from_json function)
• Removed ISSUE_ID_LOOKUP input (boolean toggle) - now lookup happens automatically when ISSUE_ID_LOOKUP_JSON is provided
• Created centralized _build_commit_message_with_trailers function to handle all trailer ordering and insertion
• Updated tests to verify lookup functionality is no longer in action steps

Reviewed Changes

Copilot reviewed 16 out of 16 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/github2gerrit/cli.py	Added _resolve_issue_id_from_json function and --issue-id-lookup-json CLI parameter; integrated lookup into main flow
src/github2gerrit/core.py	Removed legacy _insert_issue_id_into_commit_message; added centralized _build_commit_message_with_trailers for consistent trailer management
src/github2gerrit/models.py	Added issue_id_lookup_json field to Inputs dataclass
action.yaml	Removed ISSUE_ID_LOOKUP input and JSON lookup steps; added GITHUB_ACTOR environment variable; disabled UV cache
.github/workflows/github2gerrit.yaml	Removed ISSUE_ID_LOOKUP input from workflow definitions
README.md	Updated documentation to reflect automatic lookup behavior and removed migration note
tests/*.py	Added issue_id_lookup_json="" to all test Inputs instantiations; updated action step tests

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