perf(files): map launcher file result commands by path

[JustYannicc]

What changed

• Builds a first-match Map from launcher file result paths to their generated commands.
• Uses that map when assembling root-search file candidates instead of scanning fileResultCommands with .find for each result.
• Extracts the file-candidate assembly into a focused utility and adds a 3000-result node --test harness.

Why

Launcher file candidate assembly can receive up to 3000 file results. Looking up each result command with .find makes that path O(n^2), while a path map keeps the assembly O(n) and preserves the existing path matching behavior.

Compatibility impact

No launcher behavior is removed. File result order, strict path matching, command data, scoring, and missing-command fallback behavior are preserved. Duplicate command paths continue to use the first command, matching the old .find semantics.

How tested

• Baseline lookup micro-benchmark before the change, 3000 results/commands, 500 iterations: .find median 12.214ms (min 11.199, max 55.398), path map median 0.100ms (min 0.083, max 0.656), equal checksum 11445000.
• After lookup micro-benchmark using the exported map builder, 3000 results/commands, 500 iterations: .find median 18.121ms (min 17.277, max 31.698), path map median 0.024ms (min 0.023, max 0.324), equal checksum 11445000.
• node --test scripts/test-launcher-file-result-command-map.mjs on the clean PR branch: full candidate assembly map median 25.097ms vs find-backed median 45.257ms, equal checksum 99347250.
• ./node_modules/.bin/tsc -p tsconfig.renderer.json --noEmit --pretty false was run on the clean PR branch and fails on existing origin/main renderer type errors unrelated to this file-result lookup change.
• git diff origin/main --check

Stack validation

Clean branch from origin/main; this PR is one commit ahead and is not stacked on #530-#535.

[JustYannicc]

Superseded by #555, which now includes this launcher file-result command map fix and preserves the first duplicate-path command semantics/evidence.