fix: make Prompt Syntax outcomes explicit

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Summary

• make every standalone authored Prompt Syntax line resolve to either an applied directive or a typed refusal instead of silently remaining raw text
• cover the exact Codex items.state form from the reported transcript
• visually mark live Prompt Syntax directives while keeping prose-attached, quoted, indented, and fenced examples inert
• make frontend Markdown fence tracking agree with the backend for marker type and width
• reconcile the requested status when Task Manager repeats one uniquely matching item title, and refuse ambiguous legacy duplicates
• keep Task Manager and pull request mutations on the one declared Prompt Syntax surface
• show Codex writable-root approval requests as exact paths and scope remembered rules to that exact path set
• document all Task Manager working directories as declared roots and point persistent access back to Settings
• bump the workspace to 0.1.57 in an isolated commit

Verification

• cargo test --workspace (99 GUI tests)
• cargo clippy --workspace --all-targets -- -D warnings
• cargo check --workspace after the version bump
• bun run typecheck
• bun run test:run (266 tests)
• bun run build
• bun run lint

The companion Codex writable-root, mid-turn steering, and message-boundary fixes are in agent-abstraction PR #22 and will be consumed after 0.4.6 publishes.

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Superseded by #78, which now targets master and contains both the PromptSyntax fixes and the experimental-profile release.