Allow chat corrections to update notes

[ComputelessComputer]

Adds an exact correction chat tool that can update session summaries and transcripts, wires it into chat guidance, and covers replacement behavior with focused tests.

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This is part 2 of 2 in a stack made with GitButler:

•  2  Allow chat corrections to update notes #5780 👈
•  1  Search notes for unattached chat questions #5779

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Note

Medium Risk
The tool writes directly to Tinybase enhanced_notes and transcripts without undo; incorrect oldText or model misuse could corrupt user note content, though matching is exact and guards limit partial transcript updates.

Overview
Adds a new apply_session_correction chat tool so the assistant can persist user corrections (e.g. “it’s not X but Y”) into local session data instead of only replying in chat.

The tool performs exact oldText → newText replacements on enhanced note summaries (markdown round-tripped through the editor JSON) and/or transcripts (words token spans plus memo_md), scoped by session and optional enhancedNoteId, with default target summary_and_transcript. Transcript updates require words and memo to both match when both exist; blank replacements are rejected; invalid summary IDs error for summary-only targets but transcript edits can still apply on the default combined target.

It is registered in the chat tool registry with typed I/O, and FILE_CONTEXT_TOOL_GUIDANCE now instructs the model to call this tool (and read_current_note when needed) for correction phrasing. Behavior is covered by a new session-correction.test.ts suite.

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