docs: rename the RFC files to 2026-07-07-plan-mode

The trio (en, zh, i18n record) follows the plan-mode-first retitle; switcher
links, the pairing record's keys, and the generated index move with it.

docs/rfc/INDEX.md

@@ -12,7 +12,7 @@ Generated by `pnpm run gen-rfc-index` from the RFC tree — never edit by hand;
 | [Multiplex concurrent ACP sessions over one connection](proposed/feature/2026-06-14-acp-multi-session.md) | 2026-06-14 |
 | [Optional Code Mode — model writes TypeScript against an SDK of all tools](proposed/feature/2026-06-15-optional-code-mode.md) | 2026-06-15 |
 | [Pre-tool input rewrite — a consistent design](proposed/feature/2026-06-30-pre-tool-input-rewrite.md) | 2026-06-30 |
-| [Plan mode — a logged per-agent session mode](proposed/feature/2026-07-07-session-modes-plan-mode.md) | 2026-07-07 |
+| [Plan mode — a logged per-agent session mode](proposed/feature/2026-07-07-plan-mode.md) | 2026-07-07 |
 
 ### Simplification
 

docs/rfc/proposed/feature/2026-07-07-plan-mode.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
-2026-07-07-session-modes-plan-mode.md: 8ae896e62d564bc77870d7449992e9eaccf577c5
-2026-07-07-session-modes-plan-mode.zh.md: 3bde47ea5491c69f56f49e3fcff9a6eed49d52e4
+2026-07-07-plan-mode.md: 0897f66b7bdaa789c0cae2bc348690da77c6f42c
+2026-07-07-plan-mode.zh.md: 9c7b1fe6e9cb4416e67fcf242bd80d00a3e0cc45

docs/rfc/proposed/feature/2026-07-07-plan-mode.md

@@ -2,7 +2,7 @@
 
 Status: proposed
 
-English | [中文](2026-07-07-session-modes-plan-mode.zh.md)
+English | [中文](2026-07-07-plan-mode.zh.md)
 
 ## Problem
 

docs/rfc/proposed/feature/2026-07-07-plan-mode.zh.md

@@ -2,7 +2,7 @@
 
 Status: proposed
 
-[English](2026-07-07-session-modes-plan-mode.md) | 中文
+[English](2026-07-07-plan-mode.md) | 中文
 
 ## 问题