feat(course): build out all 27 modules, capstone, scaffold, and conventions

Scaffold the course repo and author the full curriculum in dependency-chain
order, following the settled build decisions in handoff.md.

- Scaffold: course README, vendor-neutral AGENTS.md (dogfoods Module 5),
  _TEMPLATE.md (the fixed 9-section module shape), root .gitignore, ship config.
- Modules 1-2: reference exemplars (locked for tone/depth/lab style).
- Modules 3-27: full lessons + runnable labs, each following the template,
  respecting the chain, vendor/model-agnostic, with "feel the pain" labs.
- Module 8 hosting comparison web-researched and date-stamped (as of 2026-06-22),
  not written from memory; expansion-zone modules carry Verify-before-publish.
- Capstone: the full loop end to end on the running tasks-app example.

Lab code syntax-checked (Python/shell/YAML); every module has the 7 core
template sections.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TfzV5QvtPDz8LJS3Pu5VLT

modules/07-worktrees-running-agents-in-parallel/lab/agent-a-prompt.md

@@ -0,0 +1,15 @@
+# Agent A prompt — the `clear` command
+
+Paste this into the AI session you've pointed at the `tasks-app-clear` worktree folder.
+
+---
+
+Add a `clear` command to this task app that removes **all** tasks.
+
+- Put the deletion logic on `TaskList` in `tasks.py` (a `clear()` method that empties the list),
+  and wire a `clear` command into the dispatch in `cli.py` that calls it and saves.
+- Running `python cli.py clear` should empty the list and print a short confirmation like
+  `cleared all tasks`.
+- After `clear`, `python cli.py list` should print `(no tasks yet)`.
+
+Make the change, then stop — I'll review the diff and commit it myself.