feat: add remote acceleration settings, consent, and active-mode indicators

[Abhash-Chakraborty]

Problem

Remote ML acceleration has privacy-sensitive UX requirements. Users must explicitly enable it, understand what data is sent, and see when remote mode is active.

Goal

Add frontend settings and indicators for optional self-hosted remote acceleration.

Scope

• Add a Remote Acceleration settings section.
• Add enable/disable toggle, server URL, API key, feature checkboxes, EXIF stripping toggle, and test connection action.
• Add first-enable consent dialog.
• Add active remote-mode indicators during processing, search, and gallery browsing.
• Warn on non-localhost HTTP endpoints.
• Warn on known Cloudflare Tunnel hostnames as documented.

Acceptance criteria

• Remote acceleration cannot be enabled without explicit consent.
• The UI clearly states that images may be sent to the configured user-owned server.
• The UI distinguishes full image transmission from vector-only clustering.
• Non-localhost HTTP endpoint warning is shown and requires acknowledgment.
• Active remote mode is visible during processing/search/gallery use.
• Settings persist through the selected app configuration mechanism.
• No remote endpoint is preconfigured.

Suggested files

• frontend/src/app/
• frontend/src/components/
• frontend/src/lib/api.ts
• docs/plans/not-started/remote-acceleration.md

[Abhash-Chakraborty]

Split out a beginner-friendly UX-copy documentation starter task from this larger remote acceleration UI issue:

• docs: add remote acceleration UX copy checklist #268

[YashKrTripathi]

Hi! @Abhash-Chakraborty I'm a GSSoC'26 contributor and I'd like to work on this issue.

My approach:

1️⃣ Settings UI — Remote Acceleration Section

• Add a new "Remote Acceleration" section in the Settings page under frontend/src/app/
• Fields/controls:
  • Enable/Disable toggle (off by default — no remote endpoint preconfigured)
  • Server URL input (with format validation)
  • API Key input (masked, with show/hide toggle)
  • Feature checkboxes — e.g. embeddings, clustering, search (granular per-feature opt-in)
  • EXIF stripping toggle (default ON for privacy)
  • "Test Connection" button → calls a helper in frontend/src/lib/api.ts and shows success/failure inline

2️⃣ First-Enable Consent Dialog

• When the user flips the enable toggle for the first time, open a modal that:
  • Explicitly states images may be sent to the configured user-owned server
  • Clearly distinguishes full image transmission vs vector-only clustering (different data exposure levels)
  • Requires the user to check an acknowledgment box before "Enable" is clickable
  • Cannot be bypassed by reloading — consent persisted in app config

3️⃣ Endpoint Safety Warnings

• Non-localhost HTTP warning: if URL is http:// and host ≠ localhost/127.0.0.1, show a blocking warning requiring explicit acknowledgment (insecure transport for image data)
• Cloudflare Tunnel hostname warning: detect known CF Tunnel domains (*.trycloudflare.com, etc. per docs) and surface a clear warning per the documentation guidance
• Both warnings must be acknowledged before save

4️⃣ Active Remote-Mode Indicators

• Add a small, persistent badge/icon (e.g. "☁ Remote Mode") visible during:
  • Processing flows
  • Search results
  • Gallery browsing
• Place it consistently (e.g. header / status bar) so users always know when their data path is remote
• Reuse a shared <RemoteModeBadge /> component for consistency

5️⃣ Persistence & API Layer

• Persist all settings via the app's existing config mechanism (no new storage layer)
• Centralize the remote-mode helpers (isRemoteEnabled, getRemoteConfig, testConnection) inside frontend/src/lib/api.ts
• Ensure feature flags drive whether each pipeline (embedding/clustering/search) actually uses the remote endpoint

6️⃣ Documentation

• Update docs/plans/not-started/remote-acceleration.md → move/update relevant sections to reflect the implemented UX (consent flow, warnings, indicators)

7️⃣ Testing

• Manual verification of every acceptance criterion (consent gate, warnings, indicators, persistence, default-off)
• Verify no remote endpoint is preconfigured on a fresh install
• Confirm settings survive reloads and respect the app's config mechanism

Scope guarantees:

• Frontend-only changes (settings UI + indicators + warnings) — no backend modifications
• Privacy-first: explicit consent + zero preconfigured remote endpoints

ETA: 3 days. Please assign this to me!