docs: add technical plan for dispute chat shared key and multimedia support

[Catrya]

Technical plan for migrating dispute chat (user-admin) from direct gift wrap encryption to shared key (ECDH), unifying it with the P2P chat mechanism, and enabling multimedia (images/files) via Blossom servers.

Phases

• Phase 1: Switch dispute chat to shared key encryption (protocol change, coordinate with admin dev)
• Phase 2: Unify message model from DisputeChat to NostrEvent (internal refactor)
• Phase 3: Render multimedia in dispute chat (decouple widgets, reuse P2P rendering)
• Phase 4: Send multimedia from dispute chat (attachment button, upload flow)
• Phase 5: Code cleanup and deduplication (extract shared utilities, remove dead code)

Each phase = 1 PR, with tests and manual testing checklist.

Full plan: docs/DISPUTE_CHAT_MULTIMEDIA_PLAN.md

Summary by CodeRabbit

• Documentation
  • Added a comprehensive roadmap for dispute chat improvements: phased rollout for shared-key encryption, unified message model, multimedia rendering and sending, attachment/encryption flows, testing and acceptance criteria, timelines, risk notes, and coordination guidance for staged deployment.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

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Walkthrough

Adds a new planning document that defines a five‑phase migration to a shared‑key (ECDH adminSharedKey) dispute chat model and phased multimedia support via Blossom servers, specifying protocol changes, data/model updates, tests, UI considerations, timelines, and coordination notes.

Changes

Cohort / File(s)	Summary
Planning document docs/DISPUTE_CHAT_MULTIMEDIA_PLAN.md	New detailed multi‑phase plan (Phases 1–5) describing migration to shared key encryption for dispute chat, unification of message model, multimedia rendering/sending via Blossom servers, encryption/attachment flows, notifier/data model updates, test lists, UI notes, timelines, risks, and coordination tasks.

Sequence Diagram(s)

sequenceDiagram
  participant Client as Client (Web/Mobile)
  participant Server as App Server
  participant Blossom as Blossom Media Server
  participant DB as Database
  participant Notifier as Notifier Service

  Client->>Server: open dispute chat / request key (ECDH)
  Server->>Client: deliver adminSharedKey (encrypted)
  Client->>Server: send encrypted text/message + attachment metadata
  Server->>Blossom: upload encrypted attachment (store & return URL)
  Blossom-->>Server: attachment URL / storage confirmation
  Server->>DB: persist message record (refs to attachment URL, crypto metadata)
  Server->>Notifier: emit message event (includes minimal metadata)
  Notifier->>Client: push notification / event
  Client->>Blossom: fetch/render encrypted attachment via signed URL (decrypt locally)

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Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Poem

🐰 A tiny plan hops into view,
Keys handshake, then blossoms too —
Phases laid out, step by step,
Media, crypto, tests adept.
A rabbit cheers this careful cue! 🌸🔐

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The PR title directly and clearly describes the main change: adding a technical plan document for dispute chat shared key encryption and multimedia support.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Merge Conflict Detection	✅ Passed	✅ No merge conflicts detected when merging into main

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch chat-user-admin

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[coderabbitai]

Actionable comments posted: 1

🤖 Fix all issues with AI agents

In `@docs/DISPUTE_CHAT_MULTIMEDIA_PLAN.md`:
- Line 89: Add language specifiers ("text") to the fenced code blocks used for
test pseudocode in DISPUTE_CHAT_MULTIMEDIA_PLAN.md; locate the eight opening
backticks that precede the test group headings (e.g., group('Dispute Shared Key
Computation'), group('p2pWrap / p2pUnwrap round-trip'),
group('DisputeChatNotifier message model'), group('Dispute chat message type
detection'), group('P2P EncryptedImageMessage regression after decoupling'),
group('Dispute chat file upload'), group('NostrUtils.sharedKeyToBytes'), and
group('MediaCacheMixin')) and change the opening ``` to ```text for each block
to satisfy markdownlint MD040.

🧹 Nitpick comments (1)

docs/DISPUTE_CHAT_MULTIMEDIA_PLAN.md (1)

76-83: Clarify the subscription approach decision.

The document presents an alternative approach for subscription management but doesn't specify which one should be implemented. Consider adding a clear recommendation or decision marker (e.g., "Recommended: Integrate into SubscriptionManager...") to help implementers choose the right path.

[grunch]

LGTM