index: split webhook into independent per-gesture configs

[derek-knox]

Note

YAGNI, but I started to sense storing multiple (3+) webhook configs being valuable where UX-wise there'd be a mechanism to enable quick swapping or additional gestures (triple click & hold, etc.).

TLDR

• Update webhooks support so each gesture (singe|double click & hold ) can be routed to a unique webhook url
• Resolved conflicts with this PR so X-Index-Trigger header is still used resulting in best of both worlds

Settings	Single gesture	Double gesture

Notes

Since the existing SecondaryMode's webhook entry (legacy id=2) is retired (Preferences.kt#L297-L298) I opted for a path that seemed to best adhere to existing conventions.

As can be seen in the above working app screenshots, the Index 01 > Settings > Advanced refactors the single webhook cta into two ctas so there is now a config per gesture.

Details

Implements the invited split-webhook feature as per-gesture webhook configs on top of the existing decorator model — the lowest-friction path that aligns with current patterns. Merged with master, so #298's X-Index-Trigger header is reconciled here (folded together) rather than reverting either side:

• IndexWebhookPreferences: independent config (URL / headers / payload mode) per gesture via new IndexWebhookGesture — which also owns the X-Index-Trigger header name + wire values (single-click-hold / double-click-hold); old IndexWebhookTrigger and Add Index trigger gesture to webhook headers #298's duplicate IndexWebhookRecordingTrigger removed
• Migration: legacy auth token → headers first, then flat config seeded into the gesture(s) the old trigger covered; flat keys removed
• RecordingOperationFactory: wraps by gesture; upload operation re-reads its gesture's config after the inner operation, so unlinking mid-processing suppresses the upload
• IndexWebhookApi: uploadIfEnabled() → upload(config, …, gesture), now a stateless client that emits X-Index-Trigger (stripping any user-set override); unused isEnabled flow removed
• Header provenance keeps Add Index trigger gesture to webhook headers #298's omit-when-unknown contract: routing uses a non-null configGesture (single-click slot); the header uses a nullable observedGesture, omitted for local (phone-mic) recordings and unrecoverable legacy retries
• Settings UI: two entry points (single / double click & hold), each independently configurable; trigger radio group removed; dialog note that X-Index-Trigger disambiguates when both gestures share a URL
• Tests: IndexWebhookPreferencesTest (12 cases: migrations, round-trips, per-gesture independence) + IndexWebhookGestureTest locks the header wire values
• Docs: INDEX_WEBHOOK_API.md setup + X-Index-Trigger sections updated

[CLAassistant]

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[ericmigi]

yup we'll definitely be adding this into settings in near future