docs: capsite AGENTS.md for agent working rules

The hard rules move from the goal tree into a proper AGENTS.md at the
capsite root (discoverable by agents without reading the tree; the
workspace AGENTS.md's commit-trailer policy stays where it is, linked).
Checklist keeps a one-line pointer, so a continuation prompt still
surfaces them. Error hygiene (no header/param values in messages)
groups with secrets discipline there rather than as its own rule.

Generated-by: opencode (GLM)

capsite-checklist.md

@@ -99,18 +99,11 @@ madmode (EmDash site; separate worker, separate concerns):
     # admin at /_emdash/admin; dev-bypass auth helper:
     # /_emdash/api/setup/dev-bypass?redirect=/_emdash/admin
 
-## Hard rules (learned 2026-10-06/07; keep them)
+## Working rules
 
-- The ASSISTANT never runs wrangler/astro dev servers; the user does
-  (assistant watches work happen via .tmp/capsite.script; one-shot
-  codegen like `wrangler types` is fine).
-- Worker secrets never in source/config; `.dev.vars` (gitignored) locally,
-  `wrangler secret put` deployed. Since the DO split, only DIIGO_WEB_ID
-  is a diigo-dump secret at all.
-- Error messages must not contain header or param values (they cross RPC
-  as exceptions and land in logs); URLs appear query-stripped.
-- `wrangler types` after any wrangler.jsonc change (generated
-  worker-configuration.d.ts is gitignored).
+Agent working rules are in [AGENTS.md](AGENTS.md) — dev servers are the
+user's job; secrets discipline; keep config types generated. They apply
+to every goal in this tree.
 
 ## Pointers