feat(career): profile passport wall, home career card, shareable PNG card (#955)

* feat(career): profile passport wall, home career card, shareable PNG card

Career v3, WS2. The identity artifact leaves the plugin tab:

- Profile: #v3-profile-passports-mount (core, one div) filled by career
  on v3:profile-rendered — per-instrument shelves of earned covers,
  hours, gig count, open-career link. Absent-not-empty.
- Home: the plugin-count stat tile becomes #v3-dash-career-slot with the
  old stat as fallback content; career replaces it with a trading-card
  tile (leather + foil shine, badge count, hours, closest-stamp ask) on
  the existing v3:dashboard-rendered event.
- Shareable card: static/js/blob-io.js (downloadBlob lifts the idiom
  duplicated verbatim in settings-io/diagnostics-export — both
  refactored; copyImageBlob wraps ClipboardItem, returns false to signal
  the download fallback). Earned passports get Save/Copy card: a
  natively-drawn 480×640 canvas (leather, stamp ring, stubs+hours line);
  copy falls back to download with a notice when the clipboard refuses.
- Mount-point convention documented in docs/plugin-v3-ui.md.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* fix(career): external surfaces stay absent until a passport exists

CodeRabbit on #955: a bare commitment produced a zero-passport wall and
replaced the dashboard fallback. Docs also now say mounts may hold
fallback content and plugins REPLACE, never append.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

docs/plugin-v3-ui.md

@@ -189,3 +189,23 @@ out of the capability graph.
 - [ ] `#player` overlays keep `z-index` ≤ the chrome layers (transport/HUD 20,
       rail 30, popovers 40).
 - [ ] Verify at `/` — it and `/v3` serve the same (and only) v3 shell.
+
+## Injecting into core shells (profile, dashboard)
+
+Core screens that accept plugin sections render **mount points** — usually
+empty, sometimes holding core's own **fallback content** (the Dashboard's
+career slot ships the plugin-count stat) — and announce each (re)build with a
+DOM event, because their `innerHTML` swap wipes anything previously injected.
+A plugin listens for the event and **replaces the mount's content** (never
+append — a fallback may be present) by id — the same seam every time:
+
+| Shell | Event | Mounts |
+| --- | --- | --- |
+| Profile | `v3:profile-rendered` | `#v3-profile-passports-mount` (career wall), `#v3-profile-feats-slot`, `#v3-profile-achievements-mount` |
+| Dashboard | `v3:dashboard-rendered` | `#v3-dash-career-slot` (career card; core's plugin-count stat is the fallback content a plugin may replace) |
+| Settings | `v3:settings-rendered` | per-plugin `settings.html` panels |
+
+Rules: inject on every event (the mount is fresh), keep the section
+**absent-not-empty** (no state → leave the mount alone / empty), and guard
+re-wired listeners with a `dataset` flag when your own refresh path can run
+against an unwiped mount.