chore(gitignore): exclude src/ build artifacts, scratch files, and .plans/

Compiled .js/.d.ts/.map files from dev builds were leaking into src/.
Also ignores preflight-script.ts (scratch WIP) and .plans/ directory.

.gitignore

@@ -2,6 +2,13 @@
 # ── Compiled test output ──
 dist-test/
 
+# ── Compiled output in src/ (should only contain .ts source) ──
+src/**/*.js
+src/**/*.js.map
+src/**/*.d.ts
+src/**/*.d.ts.map
+!src/**/*.test.js
+
 # ── GSD project state (development-only, lives in worktree branches) ──
 package-lock.json
 .claude/
@@ -42,6 +49,9 @@ tmp/
 packages/*/dist/
 packages/*/node_modules/
 
+# ── Scratch/WIP files ──
+preflight-script.ts
+
 # ── GSD baseline (auto-generated) ──
 dist/
 !/pkg/dist/modes/
@@ -55,6 +65,7 @@ TODOS.md
 .planning/
 .audits/
 docs/coherence-audit/
+.plans/
 
 # ── GSD project state (per-worktree, never committed) ──
 .gsd/