feat(memory): /smart-compact forget — safe project memory deletion

[alpertarhan]

Implements #63. Review context: #63 (comment)

What

/smart-compact forget permanently deletes the current project's graph memory.

Graph layer (forgetProjectGraph): drains the pending index queue first — a scheduled compaction state that flushes after deletion would otherwise resurrect the memory — then deletes in one transaction:

• context_nodes_fts rows for the project's nodes (the duplicated-content FTS copy — see the review comment: the FTS table is standalone, not external-content, so both copies must go)
• context_edges for the project
• context_nodes for the project

Command layer: cwd → deriveProjectIdFromCwd (same resolution as /loops), no-op notice when there is nothing to delete, then a confirmation dialog showing exactly what will be removed (node count, session count) and what is kept. TUI-only, matching the settings action pattern.

Deliberately kept: compaction state files (they power restore, they are not memory) and backups.

Why deletion is now safe

Two earlier pieces make this sound:

• fix(graph): tombstones are terminal — re-derivation cannot resurrect facts #69 (merged): tombstones are terminal — after forgetting, a later compaction that re-derives the same facts from the transcript cannot resurrect them; a fresh ingest of genuinely new content works normally.
• The paired-delete precedent (removeFtsNode + removeNode) already existed for single nodes; this is its project-scoped bulk form.

Verification

• 989 tests (2 new: forget clears nodes/edges/FTS including a direct SQLite probe of the FTS table while a sibling project stays intact; parser accepts the forget action), bench, build, release audit — all green