docs: register the est_tokens design in the research wiki

Records the approved option, the four rejected alternatives with their
reasons, the intentionally dropped CHS migration item, and the two
defects the independent review caught. Links the entry to m1-core-design
as a refinement, since that milestone is where est_tokens froze with
both jobs attached.

research-wiki/index.md

@@ -1,15 +1,17 @@
 # Research Wiki 索引
 
-> 自动生成，更新时间：2026-07-30 04:44 UTC
+> 自动生成，更新时间：2026-07-30 09:33 UTC
 
-## design (14)
+## design (16)
 - [2026-07-20-m1-core-design](designs/2026-07-20-m1-core-design.md) `design:2026-07-20-m1-core-design`
 - [2026-07-20-m2-distributed-design](designs/2026-07-20-m2-distributed-design.md) `design:2026-07-20-m2-distributed-design`
 - [2026-07-21-m25-resilience-design](designs/2026-07-21-m25-resilience-design.md) `design:2026-07-21-m25-resilience-design`
 - [2026-07-21-m3-ocr-design](designs/2026-07-21-m3-ocr-design.md) `design:2026-07-21-m3-ocr-design`
 - [2026-07-22-m4-migration-design](designs/2026-07-22-m4-migration-design.md) `design:2026-07-22-m4-migration-design`
 - [2026-07-29-settings-invariant-guards-design](designs/2026-07-29-settings-invariant-guards-design.md) `design:2026-07-29-settings-invariant-guards-design`
+- [2026-07-30-est-tokens-decoupling-design](designs/2026-07-30-est-tokens-decoupling-design.md) `design:2026-07-30-est-tokens-decoupling-design`
 - [2026-07-30-settings-invariants-round-2-design](designs/2026-07-30-settings-invariants-round-2-design.md) `design:2026-07-30-settings-invariants-round-2-design`
+- [est_tokens 解耦: 拆分限流预扣与遥测用量兜底(issue #2)](designs/est-tokens-decoupling.md) `design:est-tokens-decoupling`
 - [GatewaySettings 装配校验补齐(第二轮)](designs/settings-invariants-round-2.md) `design:settings-invariants-round-2`
 - [GatewaySettings 跨字段不变量守卫的生效范围](designs/settings-invariant-guards.md) `design:settings-invariant-guards`
 - [M1 核心里程碑设计:公共签名冻结与治理栈落地](designs/m1-core-design.md) `design:m1-core-design`