fix(framework): install deps on worktree bootstrap + legible deps-preflight at gate seam (#856)

Worker git-worktrees under a fresh `git worktree add` have empty
node_modules/.bin (pnpm workspaces do not share node_modules across
worktrees), so every gate binary (tsc/eslint/prettier/vitest) fails with
a raw `sh: 1: <tool>: not found` before the QA gate suite ever runs a
real check. That failure is indistinguishable from a genuine test/lint
failure -- a false-red gate that was responsible for 131/147 fleet
tool-errors.

- plugins/mosaic-framework/src/index.ts: the injected "Git Worktree
  Requirement" instructions now direct every worker to run
  `pnpm install --frozen-lockfile --prefer-offline` immediately after
  `git worktree add`/`cd`, before any gate is invoked.
- packages/mosaic/framework/tools/qa/qa-hook-stdin.sh: the common
  gate-entry seam (registered as the PostToolUse hook for every
  Edit/Write/MultiEdit in runtime/claude/settings.json) now preflights
  node_modules/.bin presence for JS/TS files and fails with an explicit
  "deps not installed -- run pnpm install" sentinel instead of silently
  letting a raw not-found surface downstream.
- packages/mosaic/framework/tools/qa/test-deps-preflight.sh: new
  regression harness (wired into test:framework-shell) covering missing
  node_modules/.bin, empty node_modules/.bin, populated node_modules/.bin,
  and non-JS/TS skip behavior.

Closes #856.

packages/mosaic/framework/tools/qa/qa-hook-stdin.sh

@@ -50,6 +50,21 @@ if ! [[ "$FILE_PATH" =~ \.(ts|tsx|js|jsx|mjs|cjs)$ ]]; then
     exit 0
 fi
 
+# Deps preflight (#856): this hook is the common gate-entry seam the delivery
+# cycle invokes on every Edit/Write/MultiEdit — it fires before any pnpm-based
+# gate (test/lint/typecheck/format:check) runs against the edited file. In a
+# freshly created git worktree (pnpm workspaces do NOT share node_modules
+# across worktrees), node_modules/.bin is empty until `pnpm install` has run,
+# so gate binaries (tsc/eslint/prettier/vitest) fail with a raw, illegible
+# `sh: 1: <tool>: not found` that is indistinguishable from a real failure.
+# Fail legibly here instead, before that raw error has a chance to surface.
+BIN_DIR="$PROJECT_ROOT/node_modules/.bin"
+if [ ! -d "$BIN_DIR" ] || [ -z "$(ls -A "$BIN_DIR" 2>/dev/null)" ]; then
+    echo "deps not installed — run pnpm install" >&2
+    echo "[$(date '+%Y-%m-%d %H:%M:%S')] [ERROR] deps not installed — run pnpm install ($BIN_DIR is missing or empty)" >> "$LOG_FILE"
+    exit 1
+fi
+
 # Call the main QA handler with extracted parameters
 if [ -f ~/.config/mosaic/tools/qa/qa-hook-handler.sh ]; then
     echo "[$(date '+%Y-%m-%d %H:%M:%S')] Calling QA handler for $FILE_PATH" >> "$LOG_FILE"