chore(api): remove User.prvkey field + thread-through helpers (Q1.2 Option b)

Atomic phase-1 final per design-questions Q1.2 Option (b) and the
2026-05-29T00:30Z architecture-decisions lock-in. Removing the
prvkey?: string field from the User interface flips the type system
into the pressure mechanism that forces phase-2 to start: every
remaining bucket-B sign-site (chat / forum / nostr-feed /
activities-bookmarks/RSVP / market / tasks) now fails vue-tsc until
it migrates to signEventViaLnbits() against POST /api/v1/auth/sign-event
(aiolabs/lnbits PR #29, deployed on aio-demo).

Changes:
- src/lib/api/lnbits.ts:
  - Drop `prvkey?: string` from User interface.
  - getCurrentUser(): /auth/nostr/me used to merge prvkey alongside
    pubkey; post-cascade the endpoint returns only the pubkey.
    Updated the comment + cleaned the merge object.
- src/modules/base/auth/auth-service.ts:
  - updateProfile() no longer threads `prvkey` through the merge.
    Server-side PATCH /auth publishes kind-0 via the signer per
    869f67c3; the webapp doesn't keep prvkey at all.
- src/modules/nostr-feed/components/NostrFeed.vue +
  src/modules/nostr-feed/components/ScheduledEventCard.vue:
  - Repoint the `ScheduledEvent` type import from the deleted
    `../services/ScheduledEventService` to
    `@/modules/tasks/services/TaskService`. Trivial post-#81-merge
    cleanup that fell through the dedup PR; same file exports the
    same interface.

vue-tsc --noEmit fails with 8 errors after this commit, all
TS2339 "Property 'prvkey' does not exist". The failing sites are
exactly the bucket-B targets the design doc enumerates as
phase-2 migration work:

| Failing site                                  | Bucket B kind |
|-----------------------------------------------|---------------|
| activities/composables/useBookmarks.ts:92,113 | kind 10003 (NIP-51 bookmarks) |
| activities/composables/useRSVP.ts:153,187     | kind 31925 (NIP-52 RSVP) |
| base/services/NostrTransportService.ts:100,112| kind 21000 (NIP-44 v2 RPC envelope) |
| market/composables/useMarket.ts:455           | NIP-44 gift-wrap (kind 1059) unwrap |
| nostr-feed/components/NostrFeed.vue:408       | kind 5 (deletion of own post) |

NOT caught by vue-tsc but still bucket-B (BaseService injection
pattern types `this.authService` as `any`, so optional chaining
bypasses the type check):

- chat/services/chat-service.ts:341,511,714
- forum/services/SubmissionService.ts:755,1167
- nostr-feed/services/SubmissionService.ts:769,1226
- nostr-feed/components/NoteComposer.vue:306
- nostr-feed/components/RideshareComposer.vue:423
- tasks/services/TaskService.ts:507,562,616

Those sites will runtime-fail (prvkey is undefined from the API
post-cascade) but won't surface at compile time. Phase 2's
per-module migration (Q5.2) catches them as each module flips.

The webapp WILL NOT BUILD CLEANLY after this PR merges to dev
until phase 2 lands. That's the intended trade-off per Q5.1 +
Q1.2; the broken-build interval is the design-intended pressure
mechanism to start phase 2. server-deploy's webapp-demo flake.lock
bump will fail until phase 2 lands; demo will stay on the
pre-PR-#84 webapp during that interval.

Refs:
- log:2026-05-29T00:30Z (consolidated decisions; Q1.2 Option (b)
  + Q5.1 risk: demo gap acceptable)
- log:2026-05-29T17:30Z (lnbits confirming this PR stays
  atomic-after-the-two-bucket-A PRs)
- ~/dev/coordination/webapp-design-questions.md Q1.2 + Q5.1
- Parent initiative: aiolabs/lnbits#9 (signer abstraction / bunker)
- Sibling PRs (stacked base→head): #82 → #83 → this

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/lib/api/lnbits.ts

@@ -116,12 +116,29 @@ export class LnbitsAPI extends BaseService {
 
     if (!response.ok) {
       const errorText = await response.text()
+      // Try to surface FastAPI's `{"detail": "..."}` shape; fall back to raw
+      // body for non-JSON errors. Without this, every backend error renders
+      // as a generic "API request failed: <status>" and you can't distinguish
+      // "wrong endpoint" from "expired token" from "validation failure".
+      let detail: string = errorText
+      try {
+        const parsed = JSON.parse(errorText)
+        if (parsed && typeof parsed.detail === 'string') {
+          detail = parsed.detail
+        } else if (parsed && Array.isArray(parsed.detail)) {
+          // pydantic ValidationError: take the first msg
+          detail = parsed.detail[0]?.msg ?? errorText
+        }
+      } catch {
+        // body wasn't JSON; keep the raw text in `detail`
+      }
       console.error('LNBits API Error:', {
+        endpoint,
         status: response.status,
         statusText: response.statusText,
-        errorText
+        detail,
       })
-      throw new Error(`API request failed: ${response.status} ${response.statusText}`)
+      throw new Error(`LNbits ${endpoint} ${response.status}: ${detail || response.statusText}`)
     }
 
     const data = await response.json()
@@ -192,8 +209,12 @@ export class LnbitsAPI extends BaseService {
   }
 
   async updateProfile(data: Partial<User>): Promise<User> {
-    return this.request<User>('/auth/update', {
-      method: 'PUT',
+    // aiolabs/lnbits PR #26 (gap-fill 869f67c3) wired
+    // _publish_nostr_metadata_event into PATCH /api/v1/auth
+    // (auth_api.py:546). The legacy PUT /auth/update route does not
+    // exist on the post-cascade server.
+    return this.request<User>('/auth', {
+      method: 'PATCH',
       body: JSON.stringify(data),
     })
   }