fix: consistent zero-padding and file naming across agents

- plan-phase.md: zero-pad phase number in mkdir
- roadmapper: explicit zero-padding instruction with printf
- discuss-phase workflow: use PADDED_PHASE in file paths
- planner: fix {plan}-PLAN.md -> {phase}-{plan}-PLAN.md
- researcher: fix double-path bug in git add command
- researcher: add CONTEXT.md loading from discuss-phase

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

commands/gsd/plan-phase.md

@@ -81,10 +81,11 @@ grep -A5 "Phase ${PHASE}:" .planning/ROADMAP.md 2>/dev/null
 ```bash
 PHASE_DIR=$(ls -d .planning/phases/${PHASE}-* 2>/dev/null | head -1)
 if [ -z "$PHASE_DIR" ]; then
-  # Create phase directory from roadmap name
+  # Create phase directory from roadmap name with zero-padded phase number
   PHASE_NAME=$(grep "Phase ${PHASE}:" .planning/ROADMAP.md | sed 's/.*Phase [0-9]*: //' | tr '[:upper:]' '[:lower:]' | tr ' ' '-')
-  mkdir -p ".planning/phases/${PHASE}-${PHASE_NAME}"
-  PHASE_DIR=".planning/phases/${PHASE}-${PHASE_NAME}"
+  PADDED_PHASE=$(printf "%02d" ${PHASE})
+  mkdir -p ".planning/phases/${PADDED_PHASE}-${PHASE_NAME}"
+  PHASE_DIR=".planning/phases/${PADDED_PHASE}-${PHASE_NAME}"
 fi
 ```