perf(icons): memoize Phosphor icon resolution

[JustYannicc]

Summary

• Add bounded module-level caches for Raycast icon-name lookup, Phosphor export lookup, and final Raycast-to-Phosphor resolution, including misses.
• Preserve existing alias, fuzzy, filled-weight, and fallback behavior while avoiding repeated Phosphor export scans in hot render paths.
• Add a focused resolver measurement script and cache tests for exact mappings, fallback behavior, and cache-clear assumptions.
• Add a narrow ambient declaration for the existing direct Phosphor ESM import so the TypeScript LSP can type-check the runtime.

Metrics

Command: node scripts/measure-icon-resolution.mjs

Before caching:

• exact/repeated: 20,000 calls, 37,496.837 ms, 0.533 calls/ms
• unknown-fuzzy/repeated: 1,500 calls, 4,628.764 ms, 0.324 calls/ms

After caching:

• exact/repeated: 20,000 calls, 5.085 ms, 3,933.362 calls/ms
• unknown-fuzzy/repeated: 1,500 calls, 5.453 ms, 275.074 calls/ms

Validation

• mcp__lsp.diagnostics on src/renderer/src/raycast-api/icon-runtime-phosphor.tsx: no diagnostics
• mcp__lsp.diagnostics on src/renderer/src/vite-env.d.ts: no diagnostics
• node --test 'scripts/test-*.mjs' passes; live Electron crash recovery test is skipped because Electron is not launchable here
• PNPM_CONFIG_LOCKFILE=false pnpm run build:renderer passes
• PNPM_CONFIG_LOCKFILE=false pnpm run check:i18n exits 0; it still reports pre-existing Italian missing keys: settings.ai.whisper.vocabulary, settings.extensions.appSearchScope

Risks

• Caches assume the imported Phosphor namespace and generated Raycast icon maps are immutable for the lifetime of the renderer module.
• Cache maps are bounded at 2,048 entries and clear wholesale when exceeded, so pathological streams of unique custom names trade occasional recomputation for bounded memory.

[JustYannicc]

Superseded by the consolidated renderer performance PR #533: #533. Closing this scoped source PR so review stays centralized there.