feat(syndicator-bluesky): make link text in post content clickable

[rmdes]

Fixes #948.

• getHtmlLinks(html) returns { text, url } for each absolute <a href>, with inline markup stripped from the text.
• getLinkFacets(text, links) finds each link text in the post text (in order, so repeated text maps to successive links), skips text that is itself the URL, and returns app.bsky.richtext.facet#link facets with byte offsets.
• createRichText(client, text, facets) merges them with the detected facets, dropping any that overlap one Bluesky found itself, sorted by offset.
• post() and the quote-post path pass the facets for content.html. The URL that htmlToStatusText appends is unchanged, so a post now carries both the clickable text and the trailing URL.
• Tests: unit tests for both helpers (relative links skipped, nested tags, multi-byte offsets, repeated text, URL-as-text) and for the merge; a test-network case asserts the created record has facets for both “cheese” (bytes 7–13) and the appended URL (15–37).

Verified locally: node --test packages/syndicator-bluesky/test/**/*.js 51/51, eslint and prettier clean.