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/code-mode-workspace-context.cordis.yml

@@ -1,5 +1,5 @@
-# Code Mode workspace-context snapshot recording overlay. The scenario needs
-# filesystem tools to trigger nested instruction discovery after a read.
+# Code Mode workspace-context snapshot recording overlay. The default filesystem
+# tools trigger nested instruction discovery after a read.
 - id: base
   name: '@cordisjs/plugin-include'
   config:
@@ -21,13 +21,5 @@
 
             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'
           - id: code-runtime
             name: '@deepseek-ai/dsh-code-runtime-worker'

examples/acp-agent/fs.cordis.snapshot.yml

@@ -1,5 +1,6 @@
-# Keyless filesystem snapshots apply the filesystem and replay overlays directly
-# because include patches cannot target entries behind a nested include.
+# Keyless filesystem snapshots apply the spill and replay overlays directly
+# because include patches cannot target entries behind a nested include. The
+# sandboxed filesystem stack already lives in the base cordis.yml.
 - id: base
   name: '@cordisjs/plugin-include'
   config:
@@ -9,14 +10,6 @@
         name: '@deepseek-ai/dsh-llm-deepseek'
         disabled: true
       - 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'
           - id: spill-local
             name: '@deepseek-ai/dsh-spill-local'
             config:

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'