build(frontend)!: knip drops --production; plain knip stays

The production pass (7ed2ac4e, E32) asked "is this export used by what
ships?". No real hit: its only findings were 37 exports a test imports,
answered with 36 `@internal` JSDoc tags (E34 S2) — test-only exports, not
defects. Since then it has only ever asked for another tag. The tags go
with it (36, no longer read by anything), and so do the production-only
`!…!` exclusions in knip.jsonc and their register rows. Plain knip (unused
files, exports and dependencies) keeps running in the gate.

frontend/src/lib/api/tagModes.ts

@@ -4,7 +4,6 @@
 
 /**
  * A tag category's match: "or" = a channel with ANY selected tag passes, "and" = it must carry ALL.
- * @internal exported for its test
  */
 type TagMode = "or" | "and";
 /** The three tag categories, each with its OWN independent match mode. */