fix(indent): re-indent dedent keywords as they are typed (#2582)

[sinelaw]

Fixes #2582.

Problem

Live "electric" dedent only fired for closing brackets (}). Typing a keyword that matches a language's decrease_indent_pattern — Python else:/elif/except/finally/case, Ruby/Lua/Fish/Pascal end, Bash fi/done/esac, or a user's custom token — left the line stuck at its inherited indent:

if a:
    x = 1
    else:      ← stays over-indented

The error then compounded: pressing Enter after the mis-indented else: indented the next line another level deeper, so the whole block drifted right. Dedent rules were applied only when Enter split text onto a new line, never when the keyword was typed — even though Fresh already gave } this treatment, and the docs' own decrease_indent_pattern examples (end, CLOSE) are tokens you type at the end of a block, never Enter-split.

Fix

• Add IndentRules::calculate_dedent_for_typed_char in indent_rules.rs — the keyword counterpart of the existing calculate_dedent_for_delimiter (which handles brackets). It matches the line's leading content (after the just-typed char) against the language's decrease rule and returns the target indent, aligned to the reference line one level up.
• Hook it into the character-insert path (insert_char_events) so a completed dedent keyword snaps the line one level shallower, mirroring the existing closing-bracket handle_auto_dedent.

The hook is deliberately conservative:

• only when there's no active selection and the cursor is at the end of the line's content (the way these keywords are actually typed), so it never fires while editing mid-line;
• idempotent — it no-ops when the line is already at the correct indent, so it adds no redundant undo step on subsequent keystrokes.

Only the per-language regex rules tier is touched; curly-brace languages keep their bracket-only decrease rule (their } is handled by the existing path), so nothing changes for them.

Testing

• Unit tests (indent_rules.rs): else/except/finally/case (Python, incl. nested), end (Ruby/Lua), fi/done (Bash); plus negatives — an identifier like elsewhere, an ordinary statement, a curly-brace language, and a first line with no reference above.
• End-to-end typing tests (actions.rs): drive the production Action::InsertChar pipeline key-by-key; verify else: dedents to column 0 and that the following Enter indents the body to column 4 (not the old drifted 8).
• Manual validation: ran the built fresh binary in tmux on a Python file, typed else:, and confirmed via capture-pane that the line dedents to column 0 and its body lands at column 4.
• cargo fmt, cargo clippy, and cargo check --all-targets all clean; existing indent / auto-pair / auto-indent scenario suites pass.

🤖 Generated with Claude Code

https://claude.ai/code/session_01DvjnQtGxsMn3UKywougFDd

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