feat(claude-code): manage the user's global config in the Module

Bring the declarative half of ~/.claude into modules/claude-code and apply
it when the Module is enabled: the global agent instructions (context =
./CLAUDE.md), the skills tree (skills = ./skills), the attention-bell hook,
and settings.json (model = opus plus the Stop/Notification/SessionStart
hook wiring).

Runtime state (projects, plugins, cache, history, sessions) and the
.credentials.json secret are left out, so login survives rebuilds and no
secret enters the repo. Verified against the built home-files that
~/.claude/{CLAUDE.md,settings.json,skills,hooks/attention-bell.sh} are
generated, the hook executable.

modules/claude-code/skills/improve-codebase/SKILL.md

@@ -0,0 +1,68 @@
+---
+name: improve-codebase
+description: Scan a codebase for deepening opportunities, present them as a visual HTML report, then grill through whichever one you pick.
+disable-model-invocation: true
+---
+
+# Improve Codebase
+
+Surface architectural friction and propose **deepening opportunities** — refactors that turn shallow modules into deep ones. The aim is testability and AI-navigability.
+
+This command is _informed_ by the project's domain model and built on a shared design vocabulary:
+
+- Run the `/codebase-design` skill for the architecture vocabulary (**module**, **interface**, **depth**, **seam**, **adapter**, **leverage**, **locality**) and its principles (the deletion test, "the interface is the test surface", "one adapter = hypothetical seam, two = real"). Use its terms exactly in every suggestion, per its glossary.
+- The domain language in `.claude/CONTEXT.md` gives names to good seams; ADRs in `.claude/adr/` record decisions this command should not re-litigate.
+
+## Process
+
+### 1. Explore
+
+Read the project's domain glossary (`.claude/CONTEXT.md`) and any ADRs in the area you're touching first.
+
+Then use the Agent tool with `subagent_type=Explore` to walk every top-level module or directory in scope (the whole repository, or the area the user pointed you to) — even if only briefly for the ones that turn out clean. Within each, judge friction organically rather than against a rigid checklist:
+
+- Where does understanding one concept require bouncing between many small modules?
+- Where are modules **shallow** — interface nearly as complex as the implementation?
+- Where have pure functions been extracted just for testability, but the real bugs hide in how they're called (no **locality**)?
+- Where do tightly-coupled modules leak across their seams?
+- Which parts of the codebase are untested, or hard to test through their current interface?
+
+Apply the **deletion test** to anything you suspect is shallow: would deleting it concentrate complexity, or just move it? A "yes, concentrates" is the signal you want.
+
+Zero candidates is a legitimate outcome for a genuinely clean area — but it has to follow from having looked, not from stopping early.
+
+### 2. Present candidates as an HTML report
+
+Write a self-contained HTML file to the OS temp directory so nothing lands in the repository. Resolve the temp dir from `$TMPDIR`, falling back to `/tmp` (or `%TEMP%` on Windows), and write to `<tmpdir>/architecture-review-<timestamp>.html` so each run gets a fresh file. Open it for the user — `xdg-open <path>` on Linux, `open <path>` on macOS, `start <path>` on Windows. Treat the open as best-effort: it's a no-op in a headless/sandboxed environment with no display server, so report the absolute path regardless of whether the open succeeded.
+
+The report uses **Tailwind via CDN** for layout and styling, and **Mermaid via CDN** for diagrams where a graph/flow/sequence reliably communicates the structure. Mix Mermaid with hand-crafted CSS/SVG visuals — use Mermaid when relationships are graph-shaped (call graphs, dependencies, sequences), and hand-built divs/SVG when you want something more editorial (mass diagrams, cross-sections, collapse animations). Each candidate gets a **before/after visualisation**. Be visual.
+
+For each candidate, render a card with:
+
+- **Files** — which files/modules are involved
+- **Problem** — why the current architecture is causing friction
+- **Solution** — plain English description of what would change
+- **Benefits** — explained in terms of locality and leverage, and how tests would improve
+- **Before / After diagram** — side-by-side, custom-drawn, illustrating the shallowness and the deepening
+- **Recommendation strength** — one of `Strong`, `Worth exploring`, `Speculative`, rendered as a badge
+
+End the report with a **Top recommendation** section: which candidate you'd tackle first and why.
+
+**Use `.claude/CONTEXT.md` vocabulary for the domain, and the `/codebase-design` vocabulary for the architecture.** If `.claude/CONTEXT.md` defines "Order," talk about "the Order intake module" — not "the FooBarHandler," and not "the Order service."
+
+**ADR conflicts**: if a candidate contradicts an existing ADR, only surface it when the friction is real enough to warrant revisiting the ADR. Mark it clearly in the card (e.g. a warning callout: _"contradicts ADR-0007 — but worth reopening because…"_). Don't list every theoretical refactor an ADR forbids.
+
+See [HTML-REPORT.md](HTML-REPORT.md) for the full HTML scaffold, diagram patterns, and styling guidance.
+
+Do NOT propose interfaces yet. After the file is written, ask the user: "Which of these would you like to explore?"
+
+### 3. Grilling loop
+
+Once the user picks a candidate, run `/grill` to walk the design tree with them — constraints, dependencies, the shape of the deepened module, what sits behind the seam, what tests survive.
+
+Side effects happen inline as decisions crystallize — run `/domain-modeling` to keep the domain model current as you go, even if `.claude/CONTEXT.md` doesn't exist yet:
+
+- **Naming a deepened module after a concept not in `.claude/CONTEXT.md`?** Add the term to `.claude/CONTEXT.md`. Create the file lazily if it doesn't exist.
+- **Sharpening a fuzzy term during the conversation?** Update `.claude/CONTEXT.md` right there.
+- **User rejects the candidate with a load-bearing reason?** Offer an ADR, framed as: _"Want me to record this as an ADR so future architecture reviews don't re-suggest it?"_ Only offer when the reason would actually be needed by a future explorer to avoid re-suggesting the same thing — skip ephemeral reasons ("not worth it right now") and self-evident ones.
+- **Want to explore alternative interfaces for the deepened module?** Run the `/codebase-design` skill and use its design-it-twice parallel sub-agent pattern.