fix: keep chat output in the originating note when switching notes mid-stream

[Vokinloksar]

Summary

Fixes a bug where streaming a chat response in note A and then switching the
tab to note B caused the response to be written into note B instead of note A.
Root cause: Obsidian reuses a single editor instance per tab and swaps its
document when you navigate to another note in the same tab. The chat command
captured that live editor at invocation but wrote to it asynchronously during
streaming, so once the tab switched notes, all subsequent output (and the
trailing user delimiter / inferred title) landed in the wrong note.

Changes

• Add getFileForEditor() to detect which file an editor currently displays.
• StreamingHandler verifies the editor still shows the original note before
  each write. Once the user navigates away, it sticky-redirects remaining
  output to the original file via app.vault.process() (ordered append queue).
  Live streaming is unchanged while the note stays active.
• AiProviderService threads the originating app/file through the streaming
  path and only touches the editor (cursor, error text, tool notices) when it
  still shows the target note.
• MessageService appends the trailing role::user delimiter to the original
  file when the editor has navigated away.
• Title inference now renames the captured file instead of whatever note is
  currently active (same bug class).
• Import jest in the obsidian test mock (the new runtime obsidian import
  surfaced an ESM module-scope reference).

Note

The one edge case: if you switch notes mid-stream while in at-cursor mode, the redirected text is appended to the end of the original file rather than at the old cursor position. That's intentional —
once the note isn't in the visible editor, the cursor/selection no longer exists, so end-of-file append is the only safe option. The alternative (writing at a stale cursor in a hidden document) is
exactly the corruption we're fixing.

Test plan

• yarn test — 120 passing (added StreamingHandler tests covering
  on-target writes, redirect-on-switch, and sticky redirect)
• yarn build — type-check + production bundle succeed
• yarn lint — no new errors
• Manual: prompt in note A, switch tab to note B mid-stream → response
  stays in note A; note B untouched; reopening A shows the full response.