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).

modules/11-collaboration-humans-and-agents/lab/pr-body.md

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+<!--
+  Module 11 lab — the pull request description (station 4 of the loop).
+
+  Paste this as the body when you open the PR from your branch into main. The "Closes" line is the
+  load-bearing part: replace 42 with YOUR issue number. On merge to the default branch, the host
+  closes that issue automatically and cross-links the two.
+
+  Closing keywords that work across the major hosts: Closes / Fixes / Resolves (and their
+  variants). A bare "#42" links the issue but does NOT close it on merge.
+-->
+
+## What this does
+
+Adds a `clear-done` command that removes all completed tasks. The removal logic is a new `TaskList`
+method in `tasks.py`; `cli.py` just wires up the command and reports how many tasks were removed.
+
+## How I tested it
+
+- Added a mix of pending and done tasks, ran `clear-done`, confirmed only the done ones were removed
+  and the count printed.
+- Ran `clear-done` with nothing marked done — removed 0, no crash.
+
+## Review notes
+
+Small two-file change. Check that the logic sits in `tasks.py` (not the CLI) and that the empty /
+nothing-done case is handled.
+
+Closes #42