v0.6.0: robust feed parsing, CN host coverage, Podcast Index support

[xiaoleiy]

v0.6.0 — robust feed parsing, Chinese-market host coverage, Podcast Index support

Implements the approved design spec (docs/superpowers/specs/2026-07-07-feed-robustness-podcastindex-design.md); built task-by-task from the committed plan with two-stage review per task.

Feed parsing robustness (core.py, still pure stdlib)

• Namespace-agnostic parsing by localname: RSS 2.0, RSS 1.0 (RDF), and Atom all supported; bare tags beat namespaced synonyms (<title> wins over <itunes:title> regardless of document order).
• Enclosure discovery with fallbacks: <enclosure> → audio media:content → Atom link rel="enclosure"; duplicate enclosure+media:content items (WavPub/Omny) yield exactly one episode.
• Dirty-XML sanitize-and-retry: undefined HTML entities, bare &, control chars, junk before the declaration, real UTF-16 detection (BOM + BOM-less) — CDATA-safe, unknown entities preserved, and still fails loudly on hopeless input.
• ISO-8601 pub dates (Atom/dc:date), incl. colon-less offsets normalized for py3.9.
• ximalaya.com/album/<id> links accepted directly (Ximalaya Podcast托管 RSS).
• Download guard: text/* responses (e.g. Ximalaya CDN's 200-with-7-byte-body stale-enclosure trap) now raise instead of writing garbage audio.

Podcast Index (optional, BYOK)

• Set PODCASTINDEX_API_KEY/PODCASTINDEX_API_SECRET (free) to enrich search (merged + deduped with iTunes, graceful per-backend degradation) and gain a feed-resolution fallback when the iTunes lookup has no feed.
• Without keys: behavior byte-identical, and a regression test hard-fails if PI ever touches the network credential-less.

Tests

• 20 offline feed fixtures pinning real host quirks: 忽左忽右/xiaoyuzhou, 声动早咖啡/Ximalaya, 股癌/SoundOn, 百靈果/Firstory, 半拿铁/WavPub, 疯投圈/Typlog, 科技早知道/Fireside, 大内密谈/Lizhi + Anchor/Acast/Omny/Libsyn/Transistor + synthetic edge cases (Atom, RDF, dirty entities, UTF-16, MRSS-only).
• Browser-UA invariant pinned (SoundOn/Typlog/Fireside/Lizhi CDN 403 Python-urllib).
• pytest -m network live suite (excluded by default): all 5 pass against the real hosts.
• Suite: 22 → 60 offline tests, all green; ruff clean.

Docs

• README: Podcast Index section, ximalaya input, refreshed roadmap. CHANGELOG 0.6.0 (incl. Add a --quiet flag to podpull get #3's --quiet). Integrations (SKILL.md/OpenCode/Cursor) updated. Version bumped in both __init__.py and pyproject.toml.

Rebased on main after #3 (--quiet) merged; no dependency changes (no Homebrew resource work needed).

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