Render edited messages in encrypted search results and stop URL queries failing the search

[hayaksi1]

Problem

Two correctness bugs in encrypted (Seshat) message search:

• Edited messages don't render in results (Search result in encrypted rooms doesn't render edited messages (seshat) #32356). Seshat indexes an edit
  (m.replace) as a standalone event, so a search for the edited text matches the
  edit event. The search render path has no tile for a replace relation, so the
  match silently fails to render even though it is still counted. The live timeline
  never hits this because the SDK aggregates the edit onto its target — that
  aggregation does not run in the search path.
• A URL/colon query fails the whole "All Rooms" search (Search failed: unable to search URL in All Rooms #32341). Seshat's
  full-text engine (tantivy) treats an unescaped colon as a field:value operator,
  so a query such as https://github.com is parsed as a search of the non-existent
  field https and Seshat rejects it with FieldDoesNotExist("https"). Because the
  combined (all-rooms) search awaited both legs with Promise.all, that rejection
  failed the entire search instead of falling back to the homeserver results.

Fix

All changes are confined to Searching.ts — no UX or API surface change.

• Edited messages (Search result in encrypted rooms doesn't render edited messages (seshat) #32356): a new sanitizeSeshatResults post-processes each raw
  Seshat response. It keeps the existing state_key: null strip, and additionally
  promotes a matched edit by re-keying the result to the edit's target (the original
  message id) and lifting m.new_content into place. The SDK event mapper then resolves
  the renderable original (which carries the aggregated edit in a loaded room) instead
  of the live m.replace; for an unloaded original it builds a fresh event from the
  promoted content. Promoted edits that collide with their original are de-duplicated to
  avoid a duplicate tile / React-key clash. The encryption sidecar fields that
  restoreEncryptionInfo consumes are preserved. Only the matched event is re-keyed —
  an edit appearing solely as context is left untouched.
• URL queries (Search failed: unable to search URL in All Rooms #32341): a new hardenSeshatSearchTerm phrase-wraps a term
  containing a colon so tantivy parses it literally instead of as a field operator. It
  is applied only to the local Seshat term; the homeserver leg keeps the raw term.
  Additionally, combinedSearch now runs the two legs with Promise.allSettled and
  degrades to the surviving leg if one rejects, failing only when both legs fail —
  so a query one backend can't parse no longer takes down the whole search.

Tests

Searching-test.ts adds coverage for: term-hardening (plain term, colon/URL, already-quoted
phrase, unbalanced quote, embedded quotes, and that the hardened term reaches Seshat while the
homeserver keeps the raw term); edit promotion (re-key + content lift, non-edit left alone,
context-only edit left alone, dedup of edit+original, and empty m.new_content left alone so
no blank tile); and combined-search degradation (server-only fallback, local-only fallback,
and reject only when both legs fail). The existing state_key tests still pass.

Fixes #32356
Fixes #32341

Checklist

• I have read through review guidelines and CONTRIBUTING.md.
• Tests written for new code (and old code if feasible).
• New or updated public/exported symbols have accurate TSDoc documentation.
• Linter and other CI checks pass.
• I have licensed the changes to Element by completing the Contributor License Agreement (CLA)