feat(commands): add /gsd-scan for rapid single-focus codebase assessment (#1808)

Lightweight alternative to /gsd-map-codebase that spawns a single
mapper agent for one focus area instead of four parallel agents.
Supports --focus flag with 5 options: tech, arch, quality, concerns,
and tech+arch (default). Checks for existing documents and prompts
before overwriting.

Closes #1733

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

commands/gsd/scan.md

@@ -0,0 +1,26 @@
+---
+name: gsd:scan
+description: Rapid codebase assessment — lightweight alternative to /gsd-map-codebase
+allowed-tools:
+  - Read
+  - Write
+  - Bash
+  - Grep
+  - Glob
+  - Agent
+  - AskUserQuestion
+---
+<objective>
+Run a focused codebase scan for a single area, producing targeted documents in `.planning/codebase/`.
+Accepts an optional `--focus` flag: `tech`, `arch`, `quality`, `concerns`, or `tech+arch` (default).
+
+Lightweight alternative to `/gsd-map-codebase` — spawns one mapper agent instead of four parallel ones.
+</objective>
+
+<execution_context>
+@~/.claude/get-shit-done/workflows/scan.md
+</execution_context>
+
+<process>
+Execute the scan workflow from @~/.claude/get-shit-done/workflows/scan.md end-to-end.
+</process>