Match notes and timestamp links by episode GUID, not by title #349

Problem. #315: updating from 2.15.1 to 2.20.1 broke many notes and links because note paths and episodeName= links derive from the title, and both the sanitizer and the feed's titles changed. 2.20.2 added legacy fallbacks (src/URIHandler.ts:46, src/createPodcastNote.ts:46). The feed GUID is parsed (src/parser/feedDocumentParser.ts:197) but unused for identity, so any future sanitizer change or feed retitle breaks links again.

Proposal. Write the GUID into new episode notes' frontmatter and add an optional guid= to new timestamp links. Resolve by GUID first, then fall back to today's title logic. Old links and notes keep working because URIs stay backward compatible.

Acceptance. Retitling an episode in a test feed leaves Open note and existing timestamp links working. E2E runs in real Obsidian.

Found by the PodNotes user-feedback research (Reddit, Obsidian forum, YouTube, GitHub history).