docs: add human-facing pages for the remaining 22 promoted skills

Adds a docs page for every promoted skill that lacked one, following
.agents/writing-docs.md and using docs/engineering/to-prd.md as the
worked exemplar. Covers all of engineering/ (bar to-prd, already done),
productivity/, and misc/.

Each page states its load-bearing constraint, its invocation mode and
trigger boundary, surfaces the skill's leading word, and routes back to
ask-matt so the set forms a connected router with no dead ends.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/productivity/teach.md

@@ -0,0 +1,47 @@
+Quickstart:
+
+```bash
+npx skills add mattpocock/skills --skill=teach
+```
+
+```bash
+npx skills update teach
+```
+
+[Source](https://github.com/mattpocock/skills/tree/main/skills/productivity/teach)
+
+## What it does
+
+`teach` turns the current directory into a standing teaching workspace and teaches you one topic across many sessions — devising short, beautiful, interactive lessons tied to *why* you want to learn.
+
+The load-bearing constraint: it does **not** teach from the model's own memory. Parametric knowledge is treated as untrusted; before it can teach, it gathers high-trust resources and grounds every claim in a citation. And it is stateful — the workspace remembers what you've learned, so each session picks up where the last left off rather than starting from scratch.
+
+## When to reach for it
+
+You invoke this by typing `/teach` — the agent won't reach for it on its own.
+
+Reach for it when you want to *learn* a topic over time — a language, a framework, yoga, theoretical physics — and want the sessions to accumulate rather than evaporate. It is not for a one-off explanation; if you just need something clarified in the moment, ask directly. Reach for `teach` when the learning is a project.
+
+## Prerequisites
+
+`teach` builds a whole directory in place, so run it somewhere you're happy to keep as a dedicated workspace. Over time it writes:
+
+- `MISSION.md` — the reason you're learning this, which grounds everything else. If it's empty, `teach`'s first job is to question you until it isn't.
+- `RESOURCES.md` — the vetted, high-trust sources it teaches from.
+- `./lessons/*.html` — the numbered, self-contained lessons (the primary unit of teaching).
+- `./reference/*.html` — compressed cheat-sheets, algorithms, glossaries you'll return to.
+- `./learning-records/*.md` — what you've learned, ADR-style, used to judge what to teach next.
+- `./assets/*` — reusable components (a shared stylesheet first) so the lessons look like one course.
+- `NOTES.md` — your teaching preferences.
+
+## Mission, and the zone of proximal development
+
+Every lesson hangs off the **mission**. Without it, knowledge has nothing to attach to and lessons feel abstract — so the mission is the first thing `teach` pins down and keeps updating as you grow. From the mission and your learning records it computes your **zone of proximal development**: the next lesson should challenge you *just enough*, no more.
+
+## Storage strength, not fluency
+
+The word to think with is **storage strength** — long-term retention — as opposed to **fluency**, the in-the-moment recall that feels like mastery but isn't. `teach` deliberately builds the former through desirable difficulty: retrieval practice, spacing, and interleaving. Knowledge is taught first (where difficulty is the enemy), then skills are drilled through a tight feedback loop (where difficulty is the tool).
+
+## Where it fits
+
+`teach` is a reach-for-it-anytime standalone — a long-running learning project you drive session by session, not a step in a build chain. It shares no workflow with the other productivity skills; it simply owns its workspace directory and lives there. When you're unsure which skill or flow fits, [ask-matt](https://aihero.dev/skills-ask-matt) routes you.