feat: implement history mode and AI development logging

- add dedicated history mode UI (toggle with `h`)
- allow navigation inside history with arrows
- allow selecting history entries with Enter
- add tests for history mode behavior
- introduce AI development logs (`ai-worklog.md`, `ai-prompts.md`)
- add AI worklog policy to `instructions-agent.md`

instructions-agent.md

@@ -59,3 +59,27 @@ Agent rules:
 3. If the specification conflicts with a previous assumption, the specification takes precedence.
 4. Keep implementation aligned with the MVP scope unless explicitly asked to extend it.
 5. After code changes, run the appropriate validation workflow defined by this repository.
+
+## AI Worklog Policy
+
+This repository maintains an AI-assisted development log.
+
+Files:
+- `docs/ai-worklog.md`
+- `docs/ai-prompts.md`
+
+Rules:
+1. After every significant `plan` or `build` task, append a concise worklog entry to `docs/ai-worklog.md`.
+2. Each worklog entry must include:
+   - date
+   - task type (`plan` or `build`)
+   - short objective
+   - files inspected or modified
+   - key decisions
+   - validation commands run
+   - result
+   - unresolved issues if any
+3. When a prompt meaningfully changes architecture, behavior, workflow, debugging direction, or project structure, append the prompt (or a concise cleaned version of it) to `docs/ai-prompts.md`.
+4. Do not store private chain-of-thought or internal reasoning.
+5. Store only concise, user-facing summaries of what was done.
+6. Keep entries chronological and easy to scan.