v0.6.0 - Hardened Pagination, Provenance & Request Shields

Fixed

• Public Web Fetches Fully Shielded (#6): get_public_web now executes its entire flow (cookie tier → curl_cffi → httpx retries) under the global concurrency semaphore and the aggregate 14-second time budget, mirroring OAuth requests.
• Graceful Malformed Page Tokens (#8): Invalid page_token values in extract_public_opinion now return a structured degraded response with restart instructions instead of escaping as raw internal errors; offset parsing is strictly validated.
• Trends Fallback Provenance (#7): analyze_niche_trends now reports which tier served the data (arctic_shift / rss) with tier-specific messaging.

Changed

• Persistent Auth HTTP Client (#5): RedditAuthManager reuses a single persistent httpx.AsyncClient across token fetches/refreshes (no more connection pool leaks), with full lifecycle cleanup chained through client teardown.