fix(completion): stop callout completions recurring over block-quote prose

[Feel-ix-343]

Summary

Callout (admonition) completions kept popping up over ordinary prose inside a block quote — e.g. typing > We're going to have to decide re-showed the full [!note]/[!warning]/… list on every keystroke. They should only appear where an Obsidian callout could actually be typed (right after the > marker), not after a word is written.

Root cause in CalloutCompleter::construct: it matched the whole line against ^(> *)+, ignoring the cursor and anything after the prefix. Since the server registers " " and ">" as completion trigger characters (main.rs), every space inside a block quote re-fired the completer and it unconditionally returned all 27 callouts.

Fix: slice the line to the cursor (mirroring link_completer's line_to_cursor) and only fire when the text after the (> *)+ prefix is empty or a partial callout opener:

// before: matched the entire line, cursor-blind
Regex::new(r"^(?<preceding>(> *)+)").captures(&whole_line)?

// after: cursor-aware; must end right after a partial opener
let line_to_cursor = line_chars.get(0..character)?;
Regex::new(r"^(?<preceding>(> *)+)\[?!?[\w-]*$").captures(line_to_cursor)?

So completions still fire at > , > [, > [!, > [!no, and bare > no, but are suppressed once a space, apostrophe, or finished word appears (> note , > We're …). Nested block quotes (>> ) and the existing nested_level / preceding_text behavior are unchanged. The trigger test is extracted into a pure callout_trigger(line_to_cursor) helper with unit tests.

Test plan

• cargo test — 78 passing, incl. 4 new callout_completer tests (marker fires; opener-typing fires; prose/space/apostrophe suppressed; non-blockquote rejected).
• cargo fmt --all -- --check clean; cargo build --locked succeeds.

Link to Devin session: https://app.devin.ai/sessions/cd5d29cf010f4708bdf1a5146f8f3665
Requested by: @Feel-ix-343

[devin-ai-integration]

🤖 Devin AI Engineer

I'll be helping with this pull request! Here's what you should know:

✅ I will automatically:

• Address comments on this PR. Add '(aside)' to your comment to have me ignore it.
• Look at CI failures and help fix them

Note: I can only respond to comments from users who have write access to this repository.

⚙️ Control Options:

• Disable automatic comment, CI, and merge conflict monitoring