chore: add project documentation framework

.project-docs/05-agent-entry/context-checklist.md

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+# Context Checklist
+
+Before planning, confirm:
+
+- I know the task ID, mode, branch, worktree, base commit, and ownership result.
+- I read the active task record and know its scope.
+- I know what this project is and what it is not.
+- I treat current-state as the last integrated snapshot rather than live concurrent state.
+- I checked active decisions and the architecture overview.
+- I identified task-specific docs that need deeper reading.
+- I inspected other local task records through `task_context.py status --json`.
+- I assessed code overlap separately from semantic or decision conflict.
+- I reported missing peer records as unknown coordination state.
+- I can name unknown, stale, or conflicting information.
+- I know which updates remain task-scoped and which require Integration Gate.