feat(tui): detect terminal color scheme and apply light-optimised palette

Squash of the linearized fix/tui-color-scheme-v2 merge and the follow-up
catalog regeneration. Renders error cause chains at every diagnostic seam
(origin/fetch-failed-diagnostics) and adds color scheme detection with a
light-terminal palette.

examples/acp-agent/workspace-context.cordis.yml

@@ -22,12 +22,3 @@
             You are a coding assistant powered by the {{model}} model. Your working directory is {{cwd}}.
 
             Verify your work by running the code or tests. Keep answers brief and factual.
-      - insert:
-          - id: fs-local
-            name: '@deepseek-ai/dsh-fs-local'
-            config:
-              cwd: !!js process.cwd()
-          - id: fs-policy
-            name: '@deepseek-ai/dsh-fs-policy'
-          - id: tool-fs
-            name: '@deepseek-ai/dsh-tool-fs'