feat(doc-standards): documentation tiers, budgets, and the ceiling gate

Standing docs accrete a paragraph per PR with nothing pushing back; the
root AGENTS.md reached 8,130 words in 50 commits with the same rule
stated two and three times. This encodes the counter-pressure:

- docs/AGENTS.md becomes the documentation standard: the tier taxonomy
  (one home per fact), target word budgets, and the slop checklist.
- verify-doc-budgets joins doc-sync: word ceilings for the six
  accretion-prone standing docs, manifest-driven, frozen at current
  sizes and ratcheted down as each doc is brought to target.
- .agents/skills/dsh-doc-standards: the thin placement/audit/red-gate
  workflow over the standard, mirroring the dsh-translate-docs split.
- RFC (implemented/process) records the decision, alternatives, and
  the first audit cycle's deferred work list.

The gate's first catch was the standard itself (1,057 > 1,000); it
ships condensed to 984 words rather than with a raised ceiling.

docs/development.i18n.yaml

@@ -2,5 +2,5 @@
 # side as of the last confirmed-consistent state. Both languages carry equal authority;
 # after editing either side, bring the other along and re-record with:
 #   pnpm run verify-translation-pairing --write
-development.md: 3e11ae594759e6251e46f3bf9e0b021d9e1555c5
-development.zh.md: e8cea20a713767411304c2a3c97099004b9392c3
+development.md: 28babca2b59c844690750d767c242c08c37bf702
+development.zh.md: b34c52cebd3f333b6554ca2b5ebd66463e436572