feat(playbook): format inline code while editing

[edwin-zvs]

Summary

• render completed single-backtick Playbook spans as highlighted inline code without visible delimiters in both TUI and web editors
• preserve exact source Markdown and source offsets; Backspace at the formatted span boundary removes only the closing backtick and reveals the opening delimiter plus editable text
• keep unmatched openings and multi-backtick runs literal, and cover the new transformation in the TUI paint/cursor differential corpus
• record the durable editing rule in spec 0203 and update the built-in-template guidance

Source-preserving behavior

The stored and synchronized document remains exact Markdown, including both backticks. The rendered form is only presentation. In the web contenteditable, a completed span is atomic until Backspace at its right edge unwraps it to the opening-backtick editing form; retyping the closing backtick formats it again. This preserves the source invariant while providing the requested editing path.

Validation

• cargo test -p construct-cli playbook_inline_code — passed
• cargo test -p construct-cli playbook_backspace_after_inline_code — passed
• cargo test -p construct-cli playbook_cursor_math_matches_painted_buffer_differential — passed
• cargo test -p construct-e2e --test playbook_view -- --nocapture — passed, 8 tests
• cargo test -p construct-e2e --test playbook_view web_playbook_view_full_parity -- --exact --nocapture — passed after the native-undo-path refinement
• cargo build — passed for the full workspace

Failed commands / known baseline issue

• cargo test -p construct-cli playbook_inline_code --lib — command-shape error: construct-cli has no library target; rerun without --lib passed.
• cargo test -p construct-cli — 1,417 passed and 1 failed: color::tests::truecolor_backend_still_emits_rgb expected 38;2;92;103;118, while the captured backend output contained no RGB sequence.
• cargo test -p construct-cli color::tests::truecolor_backend_still_emits_rgb -- --exact — reproduced the same unrelated terminal-color failure in isolation. No changed file is in the color backend.
• Initial sandboxed git fetch origin main and git restore attempts were denied access to worktree Git metadata; both were rerun with the required approval and succeeded.

Reviewer media

No new recording was made. Media would not materially improve review: the dynamic boundary behavior is exercised in real headless Chromium, and the visual treatment is a small inline highlight rather than a layout change.