fix: Codex description limit + wrong-repo bug

Move skill routing table from root SKILL.md.tmpl description (1017/1024
chars) to body where there's no length limit. Add 900-char warning
threshold test. Add -C flag to all codex exec calls so Codex always
runs in the correct git root directory.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

autoplan/SKILL.md.tmpl

@@ -204,7 +204,7 @@ Override: every AskUserQuestion → auto-decide using the 6 principles.
   What alternatives were dismissed too quickly? What competitive or market risks are
   unaddressed? What scope decisions will look foolish in 6 months? Be adversarial.
   No compliments. Just the strategic blind spots.
-  File: <plan_path>" -C "$(git rev-parse --show-toplevel)" -s read-only --enable web_search_cached`
+  File: <plan_path>" -s read-only --enable web_search_cached`
   Timeout: 10 minutes
 
   **Claude CEO subagent** (via Agent tool):
@@ -315,7 +315,7 @@ Override: every AskUserQuestion → auto-decide using the 6 principles.
   accessibility requirements (keyboard nav, contrast, touch targets) specified or
   aspirational? Does the plan describe specific UI decisions or generic patterns?
   What design decisions will haunt the implementer if left ambiguous?
-  Be opinionated. No hedging." -C "$(git rev-parse --show-toplevel)" -s read-only --enable web_search_cached`
+  Be opinionated. No hedging." -s read-only --enable web_search_cached`
   Timeout: 10 minutes
 
   **Claude design subagent** (via Agent tool):
@@ -380,7 +380,7 @@ Override: every AskUserQuestion → auto-decide using the 6 principles.
   CEO: <insert CEO consensus table summary — key concerns, DISAGREEs>
   Design: <insert Design consensus table summary, or 'skipped, no UI scope'>
 
-  File: <plan_path>" -C "$(git rev-parse --show-toplevel)" -s read-only --enable web_search_cached`
+  File: <plan_path>" -s read-only --enable web_search_cached`
   Timeout: 10 minutes
 
   **Claude eng subagent** (via Agent tool):