Long chats stay fast; search in a chat; media overview

Performance (measured with 5,900 messages: open 9 s -> 0.7 s, typing 440 ms -> 25 ms)
- GET /sessions/{id}?limit=N loads the end of a chat (from the last summary
  on, at most N); /sessions/{id}/messages?before|after|around loads more
  (scrolling up stops at a summary unless asked). Without parameters the
  full history as before (terminal client).
- Chat view: memoised message list (typing, streaming and status changes no
  longer re-render the history), finished turns fold into "N steps · M files"
  with the answer visible, tool card bodies and summaries are built only when
  opened, scroll-to-bottom only when content changes.

Search: /sessions/{id}/search over the whole chat; a hit loads its part
(around) and marks the message, "back to the latest messages" returns.

Media: /sessions/{id}/media lists images, videos and audio of a chat and its
subagents (generated images, tool output, files written, media in answers,
attachments); ⋯ -> Media shows them with filters, a large view and a jump to
the message.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

CHANGELOG.md

@@ -3,6 +3,25 @@
 All notable changes to CodeCraft. Versions follow [Semantic Versioning](https://semver.org/);
 until 1.0, minor versions may contain breaking changes.
 
+## [Unreleased]
+
+### Added
+
+- **Search in a chat:** the magnifier in the chat's top bar searches all of it (messages, tool
+  output) on the server; a hit loads its part of the chat and marks the message.
+- **Media of a chat:** *⋯ → Media* shows every image, video and audio file of the chat and its
+  subagents – generated images, screenshots, files the agent wrote, media in answers, your
+  attachments – filterable, large view, "show in chat" jumps to the message.
+
+### Changed
+
+- **Long chats stay fast:** a chat opens with its messages since the last summary (at most 200);
+  older ones load when scrolling up, the history before a summary on request. Finished turns
+  fold into one line ("42 steps · 3 files", the answer stays visible). Typing, streaming and
+  status changes no longer re-render the whole history, and tool output is only built when a
+  card is opened. Measured with a chat of 5,900 messages: opening 9 s → 0.7 s (phone-like
+  CPU: 22 s → 1 s), typing 440 ms → 25 ms per key.
+
 ## [v202611-00018] – 2026-11-10
 
 ### Added