docs: add canonical glossary + install mattpocock skills adapted for repo

docs/glossary.md is the shared vocabulary source for humans and agents.
Resolves every cross-cutting term used in this repo (feature, use case,
manifest, slice, conformance, dispatch, ...) with one-sentence definitions,
relationships, and flagged ambiguities. Linked from CLAUDE.md "Read First"
and AGENTS.md preamble so every session loads it early.

.claude/skills/ installs four mattpocock skills adapted to this monorepo:
  - to-prd: writes to docs/work/prds/ with the repo's PRD frontmatter +
    merged user-stories/implementation/testing sections
  - grill-with-docs: points at docs/decisions/ + docs/glossary.md; adds
    feature.manifest.ts + conformance-rule cross-checks
  - grill-me: minor — adds pnpm work / fallow / manifest shortcuts
  - handoff: adds the repo's specific don't-duplicate artifacts list

Also fixes a missed "Phase-1" residual in CLAUDE.md's Read First section.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.claude/skills/handoff/SKILL.md

@@ -0,0 +1,36 @@
+---
+name: handoff
+description: Compact the current conversation into a handoff document for another agent to pick up. Use when the user wants to transition work to a fresh session, switch worktrees, or hand off to a subagent.
+argument-hint: "What will the next session be used for?"
+---
+
+Write a handoff document summarising the current conversation so a fresh agent can continue the work. Save it to a path produced by `mktemp -t handoff-XXXXXX.md` (read the file before you write to it).
+
+Suggest the skills the next session should use, if any. In this repo, the common follow-ups are:
+
+- `grill-with-docs` — stress-test the plan before coding
+- `to-prd` — materialize the plan into `docs/work/prds/<date>-<slug>.prd.md`
+- `superpowers:writing-plans` — author the implementation plan
+- `superpowers:subagent-driven-development` — dispatch implementer + reviewer subagents per task
+
+## Don't duplicate
+
+Reference these artifacts by path or URL rather than inlining their content:
+
+- PRDs (`docs/work/prds/*.prd.md`), epics (`docs/work/<epic>/_epic.md`), stories (`_story.md`), tasks (`*.task.md`)
+- ADRs (`docs/decisions/adr-NNN-*.md`)
+- AGENTS.md and CLAUDE.md (the next agent loads these automatically)
+- `_state.json` (orchestrator-derived; the next agent regenerates it from markdown via `pnpm work rebuild-state`)
+- Commit messages, diffs, PR descriptions — link the SHA / PR number
+- Existing plans under `docs/superpowers/plans/`
+
+## Do capture
+
+- The active **goal** in one sentence
+- **In-flight branch / worktree** and any uncommitted state (e.g. `git status` summary, dangling commits)
+- **Decisions made in conversation** that haven't yet landed in a PRD or ADR
+- **Blockers** and proposed next steps
+- **Skills to invoke first** in the next session
+- If the user passed arguments, treat them as the next session's focus and tailor the doc accordingly
+
+Keep the document short — it's a baton, not a thesis.