chore: add .project_modules.txt for repo-specific modules

[stranske]

Summary

Adds .project_modules.txt to specify repo-specific first-party modules that should not be flagged as undeclared dependencies.

Problem

diff_holdings.py and embeddings.py are standalone Python files in the repo root. The sync_test_dependencies.py script excludes root-level .py files from auto-detection, so they get flagged as undeclared dependencies.

This has caused recurring CI failures after workflow syncs.

Solution

Create .project_modules.txt with:

diff_holdings
embeddings

Requires: stranske/Workflows#441 (adds support for reading this file)

Once Workflows#441 is merged and synced, this file will prevent future breakage.

[github-actions]

Status | ✅ no new diagnostics
History points | 0
Timestamp | 2026-01-01 20:47:05 UTC
Report artifact | autofix-report-pr-123
Remaining | ∅
New | ∅
No additional artifacts

[github-actions]

🤖 Keepalive Loop Status

PR #123 | Agent: Codex | Iteration 0/5

Current State

Metric	Value
Iteration progress	[----------] 0/5
Action	wait (missing-agent-label)
Gate	success
Tasks	0/0 complete
Keepalive	❌ disabled
Autofix	❌ disabled

🔍 Failure Classification

| Error type | infrastructure |
| Error category | resource |
| Suggested recovery | Confirm the referenced resource exists (repo, PR, branch, workflow, or file). |

[Copilot]

Pull request overview

This PR adds a .project_modules.txt configuration file to declare repo-specific first-party modules that exist outside the standard package structure, preventing them from being flagged as undeclared dependencies during CI workflow syncs.

• Adds .project_modules.txt with diff_holdings and embeddings module declarations
• Prevents recurring CI failures caused by auto-detection excluding root-level Python files