Feat/perplexity plugin (#138)

* feat: add Perplexity plugin with usage analytics and local cache support

* feat: enhance SQLite for dbs using CFNetwork cache

* feat: handle unavailable usage analytics in plugin and add corresponding test

* fix: correct brand color in plugin.json and update icon.svg fill color

---------

Co-authored-by: Robin Ebers <robin.ebers@gmail.com>

Author: garanda21

docs/providers/perplexity.md

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+# Perplexity
+
+> Uses Perplexity macOS app session data from local cache (no manual configuration).
+
+## Overview
+
+- **Protocol:** HTTPS (JSON)
+- **Auth:** Bearer token extracted from local Perplexity app cache request object
+- **Data sources:**
+  - `Cache.db` (local CFNetwork cache) for token + app headers
+  - REST API for balance + usage analytics
+
+## Local Session (Required)
+
+1. Install the Perplexity macOS app.
+2. Open the app and sign in once.
+
+The plugin checks for the Perplexity cache DB at:
+
+- `~/Library/Containers/ai.perplexity.mac/Data/Library/Caches/ai.perplexity.mac/Cache.db`
+- fallback: `~/Library/Caches/ai.perplexity.mac/Cache.db`
+
+It reads the cached request object for:
+
+- `https://www.perplexity.ai/api/user`
+
+Then extracts the cached request's `Authorization: Bearer ...` token (and app-like headers).
+
+If no local session is found, the plugin throws:
+
+- `Not logged in. Sign in via Perplexity app.`
+
+## Balance + Usage (No Env Vars)
+
+When a bearer token is present in the cache DB, the plugin calls:
+
+- `GET https://www.perplexity.ai/rest/pplx-api/v2/groups` (resolve `<api_org_id>`)
+- `GET https://www.perplexity.ai/rest/pplx-api/v2/groups/<api_org_id>` (read `customerInfo.balance`)
+- `GET https://www.perplexity.ai/rest/pplx-api/v2/groups/<api_org_id>/usage-analytics` (sum `cost`)
+
+## Output
+
+- **Plan**: `Pro` when `customerInfo.is_pro === true`
+- **Usage** (single progress bar line):
+  - `limit = customerInfo.balance`
+  - `used = sum(usage-analytics[].meter_event_summaries[].cost)`
+  - `resetsAt` not set (UI shows `$<limit> limit`, no reset countdown)
+
+## Limitations
+
+- Cache format is app-version dependent and may change.
+- The REST endpoints used are not a public usage API (may change or break without notice).
+- Some REST endpoints may be protected by Cloudflare; the plugin sends app-like headers from the cached request object, but may still be blocked (usage will be unavailable).