fix(cli): add source-scoped unmine command

[MichaelWave369]

Addresses the recovery half of #2213.

#2213 reports two separate problems:

1. project-mode mining can file overlapping/duplicate content under different filenames;
2. once a bad/duplicate source is filed, there is no supported source-scoped way to remove it.

This PR intentionally fixes only (2). It does not define a project-miner content-dedup policy.

Adds:

• mempalace unmine <source-file> with dry-run by default;
• --apply required to actually remove data;
• optional --wing scope for a source intentionally filed into multiple wings;
• exact source_file matching only — no fuzzy/similarity deletion;
• removal of matching drawers, conversation registry sentinels, and closets;
• execution under the existing palace writer lock;
• WAL receipts under unmine_source.

Why this slice:
Current conversation mining already has (wing, content_hash) dedupe for re-exported conversations (commit 54397a5), but #2213's concrete case used --mode projects. Applying chunk/content dedupe to project mode needs a separate semantics decision because identical text in two project files can be legitimate. A precise recovery command is useful independently and does not pre-commit that policy.

Example:

• mempalace unmine /path/to/duplicate-export.md reports what would be removed.
• mempalace unmine /path/to/duplicate-export.md --apply removes exactly that source.
• --wing demo narrows it further.

Validation against current develop (639c69a):

• python -m pytest -q tests/test_sync.py — 43 passed
• python -m mempalace.cli unmine --help
• root CLI help contains unmine
• ruff check mempalace/sync.py mempalace/cli.py tests/test_sync.py
• ruff format --check mempalace/sync.py mempalace/cli.py tests/test_sync.py
• python -m compileall -q mempalace/sync.py mempalace/cli.py tests/test_sync.py

One clean commit, only:

• mempalace/cli.py
• mempalace/sync.py
• tests/test_sync.py

I am deliberately leaving #2213 open for the project-mode ingest-dedupe half.