Add gate intensity modes: full, lean, and solo review control

Adds a --review flag to all 13 gate-using skills and a global
production/review-mode.txt config (set during /start). Full runs all
director gates, lean skips per-skill gates but keeps phase gates, solo
skips all directors. Documents modes in director-gates.md, WORKFLOW-GUIDE.md,
and README.md.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.claude/skills/gate-check/SKILL.md

@@ -1,7 +1,7 @@
 ---
 name: gate-check
 description: "Validate readiness to advance between development phases. Produces a PASS/CONCERNS/FAIL verdict with specific blockers and required artifacts. Use when user says 'are we ready to move to X', 'can we advance to production', 'check if we can start the next phase', 'pass the gate'."
-argument-hint: "[target-phase: systems-design | technical-setup | pre-production | production | polish | release]"
+argument-hint: "[target-phase: systems-design | technical-setup | pre-production | production | polish | release] [--review full|lean|solo]"
 user-invocable: true
 allowed-tools: Read, Glob, Grep, Bash, Write
 context: fork
@@ -37,6 +37,11 @@ The project progresses through these stages:
 
 **Target phase:** `$ARGUMENTS[0]` (blank = auto-detect current stage, then validate next transition)
 
+Also extract `--review [full|lean|solo]` if present. Note: in `solo` mode,
+director spawns (CD-PHASE-GATE, TD-PHASE-GATE, PR-PHASE-GATE) are skipped —
+gate-check becomes artifact-existence checks only. In `lean` mode, all three
+directors still run (phase gates are the purpose of lean mode).
+
 - **With argument**: `/gate-check production` — validate readiness for that specific phase
 - **No argument**: Auto-detect current stage using the same heuristics as
   `/project-stage-detect`, then validate the NEXT phase transition