fix(web): discard new citations when cancelled

[Neel2107]

Cancelling a newly selected citation closed the comment popover but left its chip in the composer. Cancel, Escape, and outside dismissal now discard the pending citation and restore the original draft, including its spacing. If the draft changed meanwhile, only the pending citation is removed. Cancelling a comment edit on a saved citation preserves the citation and its original comment.

Closes #10379.

Validation:

• Added five regression cases using the real composer and Lexical editor, covering empty and existing drafts, saved citations, and edits made after insertion.
• All 57 focused tests passed across the composer and citation source suites.
• Web typecheck, targeted lint, formatting, and merge check against current main passed.
• Verified in the local desktop app: Cancel, Escape, outside dismissal, Save/Enter, and cancelling edits to a saved citation.

Model: GPT-6. Harness: Codex.

[macroscopeapp]

Approvability

Verdict: Would Approve

Macroscope's review found this PR approvable — This is a focused web bug fix that changes only citation-comment cancellation behavior, preserving existing drafts and removing unfinished citations without affecting saved citations. The implementation is localized and backed by targeted tests covering the main draft and editing scenarios.

Not approved because:

• Monthly spending limit reached (workspace setting). Approvability relies on correctness review in order to determine eligibility

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[juliusmarminge]

Superseded by #10518, which landed the same fix (remove inserted citations on cancel). Closing this as superseded — feel free to reopen if anything was missed.