[upload] Suggest one-tap hashtag chips from the user's past videos (#45)

The upload modal's Hashtags section now shows chips of the user's most-used past
hashtags ("Reuse a tag from your videos:"). Clicking one adds it to the NIP-71 't'
repeater; already-added chips dim + disable; the row is hidden for users with no
past tags.

- js/utils/hashtagSuggestions.js: pure rankHashtagsByFrequency(videos) — count =
  number of the user's videos using each tag, normalized (case + '#') and deduped
  per video, ranked by count then alphabetically. Reads video.nip71.hashtags, falls
  back to raw event 't' tags minus bitvid's fixed t=video marker.
- app.getUserHashtagSuggestions() sources the user's own videos via
  nostrService.getActiveVideosByAuthors([pubkey]) and ranks them (top 12), injected
  into the modal as getHashtagSuggestions.
- UploadModal renders the chips on open and wires clicks through the existing
  Nip71FormManager (addRepeaterEntry + setFieldValue, dedup via collectRepeaterValues).

Tests: tests/hashtag-suggestions.test.mjs (5 — per-video counting, normalization,
marker exclusion, tie-break + limit, empty input). Lint + build green.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

components/upload-modal.html

@@ -249,6 +249,10 @@
                  <!-- Hashtags -->
                 <div class="space-y-2">
                      <label class="block text-sm font-medium text-text">Hashtags</label>
+                     <div id="hashtag-suggestions-wrap" class="space-y-1 hidden">
+                        <p class="text-xs text-muted">Reuse a tag from your videos:</p>
+                        <div id="hashtag-suggestions" class="flex flex-wrap gap-2"></div>
+                     </div>
                      <div
                         class="rounded-lg border border-border/70 bg-surface/30 p-3 space-y-3"
                         data-nip71-repeater="t"