docs: Plaud comparison + feature-gap backlog

Reviews the Plaud line (Note, Note Pro, NotePin/S) to make sure the OpenScribe
roadmap covers expected capabilities, and records where OpenScribe deliberately
differs (bring-your-own-AI, self-hosted, open).

What changed:
- docs/plaud-comparison.md: feature map (Plaud vs OpenScribe status), a derived
  backlog, and what we deliberately do not copy. Sourced from Plaud's site (July 2026).
- state/TODO.md: adds a Plaud-derived backlog section (diarisation, summary templating,
  Ask-AI/RAG, custom vocabulary, multimodal, mark-a-moment, auto-title, tags/folders/
  search, share links, optional OLED display, calendar) and a pluggable-AI-providers
  milestone.

Why:
- The user asked to review Plaud for other todos; this captures them and frames the
  bring-your-own-AI differentiator that the next feature implements.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

state/TODO.md

@@ -27,6 +27,30 @@
 - [ ] M9 Hardening + OTA: API auth, credential handling, OTA update, docs handoff.
       (branch `feature/hardening-ota`)
 
+## Pending - AI provider flexibility
+
+- [~] Pluggable AI providers (server): transcription + LLM can target any open-standard
+      endpoint (OpenAI-compatible / local faster-whisper / Ollama) OR a commercial API
+      (OpenAI, Anthropic, Gemini). Config-driven, no lock-in. (branch
+      `feature/server-ai-providers`) - provider layer + HTTP providers landing now;
+      local faster-whisper wiring completes in M5.
+
+## Pending - Plaud-derived backlog (see docs/plaud-comparison.md)
+
+- [ ] Speaker diarisation + labels (server); rename-speaker in the app.
+- [ ] Summary templating: built-in templates (meeting/action-items/to-do/mind-map/
+      decisions) + user templates; role-based multidimensional summaries.
+- [ ] Ask AI: chat grounded in a recording's transcript (RAG), via the chosen LLM provider.
+- [ ] Custom vocabulary / prompt hints for transcription + summary.
+- [ ] Multimodal attachments: text notes + images attached to a recording.
+- [ ] Mark-a-moment: device long-press during recording -> highlight timestamp, surfaced
+      in the app and used to focus summaries.
+- [ ] Auto title + auto formatting of transcripts and summaries.
+- [ ] Library organisation: tags, folders, full-text search (server + app).
+- [ ] Share links for summaries (extends the export endpoint).
+- [ ] Optional hardware variant with a small OLED status display (InstantView equivalent).
+- [ ] Calendar integration (nice-to-have).
+
 ## Done
 
 - [x] Dev testing + emulation harness - native unit tests (wav/range), Wokwi emulator,