Move `type Sub` + `PLEX_SUB_URL` out of the 538-line PlexBrowse into a small
plexSubUrl.ts so the encode/decode round-trip and its guards can be unit-tested
without dragging the component (and its lazy hls.js player) into the test graph.
Pure code motion — PlexBrowse imports the two symbols; the `SubviewUrl` import
moves with them.
Tests lock: encode of each bookmarkable kind, grid/player → null, encode→decode
identity, a person name containing ':' round-tripping, and the decode guards
(positive-integer playlist id; season needs both ids; non-empty show/info/person
arg; unknown kind/garbage → null).
12 tests; full FE gate green (tsc/eslint/prettier/knip).
peter
0401dae689