chore(skills): include pcbjam-shared in the git-feature workflow

The pcbjam repo's own git-feature skills + scripts/git-workflow predated the
web/pcbjam-shared submodule and only covered root+kicad+wxwidgets. Add the MIT
contract repo as a fourth member everywhere:

- repos.sh: pcbjam_shared key (path web/pcbjam-shared, main `main`) + layout doc.
- assert-clean.sh / for-each-repo.sh: count-agnostic wording.
- git-feature-start/commit/sync/finish SKILL.md: pcbjam-shared in the branch /
  commit (kicad, wxwidgets, pcbjam-shared, then root) / rebase (root first) /
  finish orders; root pointer-bump staging + diff now include web/pcbjam-shared,
  and the root stage step excludes it like the other submodule trees.

Mirrors the root pcbjam-private skills, which already covered shared.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

scripts/git-workflow/assert-clean.sh

@@ -1,5 +1,5 @@
 #!/bin/bash
-# Exit 0 if all 3 repos are clean (no staged, no unstaged, no untracked files).
+# Exit 0 if all repos are clean (no staged, no unstaged, no untracked files).
 # Exit 1 with a readable message listing the dirty repos otherwise.
 # Untracked files count as dirty - this is intentional: starting a new feature
 # while you have uncommitted new files is almost always a mistake.
@@ -20,7 +20,7 @@ for repo in "${REPOS[@]}"; do
 done
 
 if [ ${#dirty[@]} -eq 0 ]; then
-    echo "All 3 repos clean."
+    echo "All ${#REPOS[@]} repos clean."
     exit 0
 fi
 

scripts/git-workflow/for-each-repo.sh

@@ -1,5 +1,5 @@
 #!/bin/bash
-# Run a git command in each of the 3 repos. Echoes before each run.
+# Run a git command in each repo of the 4-repo tree. Echoes before each run.
 # Usage: ./for-each-repo.sh <git-subcommand-and-args>
 #   e.g. ./for-each-repo.sh status --short
 #        ./for-each-repo.sh fetch origin

scripts/git-workflow/repos.sh

@@ -1,18 +1,28 @@
 #!/bin/bash
-# Sourced library. Single source of truth for the 3-repo layout.
+# Sourced library. Single source of truth for the 4-repo layout:
+#
+#   root  = pcbjam                                main
+#   ├── kicad           (kicad/)                  wasm-port
+#   ├── wxwidgets       (wxwidgets/)              wasm-port
+#   └── pcbjam-shared   (web/pcbjam-shared/)      main   [MIT contract]
+#
+# Bash variable names can't contain '-', so pcbjam-shared's KEY is
+# `pcbjam_shared`; its path/display name keep the dash.
 # Usage: source "$(dirname "$0")/repos.sh"
 
 ROOT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")/../.." && pwd)"
 
-REPOS=(root kicad wxwidgets)
+REPOS=(root kicad wxwidgets pcbjam_shared)
 
 PATH_root="$ROOT_DIR"
 PATH_kicad="$ROOT_DIR/kicad"
 PATH_wxwidgets="$ROOT_DIR/wxwidgets"
+PATH_pcbjam_shared="$ROOT_DIR/web/pcbjam-shared"
 
 MAIN_root="main"
 MAIN_kicad="wasm-port"
 MAIN_wxwidgets="wasm-port"
+MAIN_pcbjam_shared="main"
 
 repo_path() {
     local var="PATH_$1"