Build out all 27 modules + capstone (#1)

Co-authored-by: claude <claude@jpaul.io>
Co-committed-by: claude <claude@jpaul.io>

modules/11-collaboration-humans-and-agents/lab/issue.md

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+<!--
+  Module 11 lab — the issue to file (the "contract" / station 1 of the loop).
+
+  Create a new issue on your git host. Paste the line below as the TITLE and everything under
+  "Body" as the issue description. Note the number the host assigns it (e.g. #42) — every later
+  step references it. Assign it to yourself for the first run-through.
+-->
+
+Title: Add a `clear-done` command to remove completed tasks
+
+Body:
+
+**What**
+Add a `clear-done` command to the tasks CLI that removes every task already marked done, leaving
+the pending ones untouched.
+
+**Why**
+After working through a list, the completed items pile up as noise. There's currently no way to
+clear them out short of editing `tasks.json` by hand.
+
+**Acceptance criteria**
+- `python cli.py clear-done` removes all completed tasks and keeps all pending ones.
+- It prints how many tasks were removed.
+- The removal logic lives in `tasks.py` (a `TaskList` method), not in `cli.py`.
+- Running it when nothing is done is a no-op that removes 0 tasks (no crash).