fix(core): drive-qualify aggregate rollup and duplicate keys

[githubrobbi]

Problem

Multi-drive aggregations merged per-drive identifiers as if they were global, corrupting rollup and extension-keyed results. Found live via the MCP top_folders preset returning malformed, unusable keys on a multi-drive host.

Fixes

Rollup keys (top_folders and all path/drive rollups). Group keys were bare per-drive record indices. The cross-drive merge collided buckets from different drives, and finalize resolved every key against the first drive's records — malformed folder names or record_N fallbacks, with one drive's byte totals silently folded into another's buckets. Keys now carry the drive ordinal (high 32 bits) and resolve against the drive they came from.

Duplicate composite keys. duplicates:size+ext pushed the raw per-drive extension_id: the same extension never grouped across drives, while different extensions with colliding intern ids grouped falsely. The key now hashes the interned (lowercased) extension string.

Nested rollup sub-aggregations. rollup:...,sub=terms:ext finalized without the cross-drive ExtensionMap, resolving canonical ids through a legacy per-drive fallback (wrong extension names in sub-buckets). The map is now a required parameter through the feed and finalize chains; both dead fallbacks are deleted.

Ancestor/drilldown rollups. The per-drive record_idx was applied to every scanned drive, bucketing other drives' records against arbitrary unrelated folders. RollupMode::Ancestor now names its drive (rollup:ancestor,record=N,drive=C); out-of-scope records are skipped, including in nested sub-accumulators. The wire spec gained an optional, backward-compatible drive slot; the daemon rejects ancestor specs without one (typed WireSpecError::AncestorDriveMissing).

Structure

duplicates.rs test module moved to duplicates/tests.rs (mirrors the compact_cache/tests.rs extraction) to stay under the 800 LOC policy without adding an exception.

Tests

All regression tests were verified to fail against the pre-fix code:

• top_folders_multi_drive_keys_resolve_per_drive — pre-fix, drive D's folder vanished entirely and its bytes were credited to C:\Projects
• extension_key_groups_across_drives_by_name_not_intern_id — pre-fix, the false avi/mp4 id-collision group survived while the real cross-drive jpg pair was missed
• ancestor_rollup_scoped_to_named_drive — drilldown into C:\Projects buckets only drive C records with exact byte totals
• Parser tests for the new drive= syntax and both error paths; wire conversion accept/reject tests; rollup key encode/decode round-trip and out-of-range-ordinal fallback

Gates: full workspace suite (2493 tests), lint-prod, lint-tests, rustdoc (--document-private-items --locked), doc-tests, and xwin Windows clippy all green; the full pre-push bundle passed on push.