FRO-4: persist feed alias cache invalidation

[OXeu]

Closes FRO-4
Fixes #253

Summary

• persist feed detail cache deletions for id and alias keys after prefix invalidation
• clear alias detail cache when toggling a feed's top state
• add regression coverage for unchanged-alias edits and cache-helper save ordering

Verification

• BUN_INSTALL=/tmp/bun-install BUN_TMPDIR=/tmp/bun-tmp bun test server/src/services/__tests__/clear-feed-cache.test.ts server/src/services/__tests__/feed.test.ts
• BUN_INSTALL=/tmp/bun-install BUN_TMPDIR=/tmp/bun-tmp bun --filter './server' test
• BUN_INSTALL=/tmp/bun-install BUN_TMPDIR=/tmp/bun-tmp bun --filter './server' check
• BUN_INSTALL=/tmp/bun-install BUN_TMPDIR=/tmp/bun-tmp bun --filter './client' test
• BUN_INSTALL=/tmp/bun-install BUN_TMPDIR=/tmp/bun-tmp bun --filter './client' check
• BUN_INSTALL=/tmp/bun-install BUN_TMPDIR=/tmp/bun-tmp bun --filter './client' build
• BUN_INSTALL=/tmp/bun-install BUN_TMPDIR=/tmp/bun-tmp bun run check
• BUN_INSTALL=/tmp/bun-install BUN_TMPDIR=/tmp/bun-tmp bun run format:check

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