feat(tui): per-section visibility for the details accordion

Adds optional per-section overrides on top of the existing global
details_mode (hidden | collapsed | expanded).  Lets users keep the
accordion collapsed by default while auto-expanding tools, or hide the
activity panel entirely without touching thinking/tools/subagents.

Config (~/.hermes/config.yaml):

    display:
      details_mode: collapsed
      sections:
        thinking: expanded
        tools:    expanded
        activity: hidden

Slash command:

  /details                              show current global + overrides
  /details [hidden|collapsed|expanded]  set global mode (existing)
  /details <section> <mode|reset>       per-section override (new)
  /details <section> reset              clear override

Sections: thinking, tools, subagents, activity.

Implementation:

- ui-tui/src/types.ts             SectionName + SectionVisibility
- ui-tui/src/domain/details.ts    parseSectionMode / resolveSections /
                                  sectionMode + SECTION_NAMES
- ui-tui/src/app/uiStore.ts +
  app/interfaces.ts +
  app/useConfigSync.ts            sections threaded into UiState
- ui-tui/src/components/
  thinking.tsx                    ToolTrail consults per-section mode for
                                  hidden/expanded behaviour; expandAll
                                  skips hidden sections; floating-alert
                                  fallback respects activity:hidden
- ui-tui/src/components/
  messageLine.tsx + appLayout.tsx pass sections through render tree
- ui-tui/src/app/slash/
  commands/core.ts                /details <section> <mode|reset> syntax
- tui_gateway/server.py           config.set details_mode.<section>
                                  writes to display.sections.<section>
                                  (empty value clears the override)
- website/docs/user-guide/tui.md  documented

Tests: 14 new (4 domain, 4 useConfigSync, 3 slash, 3 gateway).
Total: 269/269 vitest, all gateway tests pass.

ui-tui/src/components/messageLine.tsx

@@ -6,7 +6,7 @@ import { userDisplay } from '../domain/messages.js'
 import { ROLE } from '../domain/roles.js'
 import { compactPreview, hasAnsi, isPasteBackedText, stripAnsi } from '../lib/text.js'
 import type { Theme } from '../theme.js'
-import type { DetailsMode, Msg } from '../types.js'
+import type { DetailsMode, Msg, SectionVisibility } from '../types.js'
 
 import { Md } from './markdown.js'
 import { ToolTrail } from './thinking.js'
@@ -17,12 +17,13 @@ export const MessageLine = memo(function MessageLine({
   detailsMode = 'collapsed',
   isStreaming = false,
   msg,
+  sections,
   t
 }: MessageLineProps) {
   if (msg.kind === 'trail' && msg.tools?.length) {
     return detailsMode === 'hidden' ? null : (
       <Box flexDirection="column" marginTop={1}>
-        <ToolTrail detailsMode={detailsMode} t={t} trail={msg.tools} />
+        <ToolTrail detailsMode={detailsMode} sections={sections} t={t} trail={msg.tools} />
       </Box>
     )
   }
@@ -98,6 +99,7 @@ export const MessageLine = memo(function MessageLine({
             detailsMode={detailsMode}
             reasoning={thinking}
             reasoningTokens={msg.thinkingTokens}
+            sections={sections}
             t={t}
             toolTokens={msg.toolTokens}
             trail={msg.tools}
@@ -124,5 +126,6 @@ interface MessageLineProps {
   detailsMode?: DetailsMode
   isStreaming?: boolean
   msg: Msg
+  sections?: SectionVisibility
   t: Theme
 }