docs: document catppuccin fallback prompt and update component reference

docs/fish-config.index

@@ -191,6 +191,15 @@ logging-sentinel=#### C5 — Logging and Capture
 c6=#### C6 — Greeting and First-Run UI
 greeting=#### C6 — Greeting and First-Run UI
 
+# ── Prompt and Theme ──────────────────────────────────────────
+prompt-theme=## Prompt and Theme
+starship=### Starship
+fallback-prompt=### Catppuccin Fallback Prompt
+catppuccin-prompt=### Catppuccin Fallback Prompt
+nim-prompt=### Catppuccin Fallback Prompt
+fzf-theme=### FZF
+catppuccin-theme=### Catppuccin Mocha Syntax Highlighting
+
 # ── Section 8: Fisher Plugins ─────────────────────────────────
 plugins=# 8. FISHER PLUGINS
 fisher=# 8. FISHER PLUGINS

docs/fish-config.md

@@ -1362,7 +1362,7 @@ fish-deps manages these tools. Run `fish-deps` to check status, or
                 Rust-based tools and to build fish from source. All paths
                 are gated on type -q cargo and degrade gracefully.
     starship    Cross-shell prompt; loaded via type -q starship guard.
-                Without it fish falls back to its built-in default prompt.
+                Without it the Catppuccin nim-style fallback prompt activates.
     uv          Python package and project manager (Astral); used by the
                 fish-from-source build path in fish-deps. All consumers
                 degrade gracefully without it.
@@ -1593,7 +1593,7 @@ all of them.
     Starship prompt           fish_prompt replaced by Starship + OSC 133 markers
     Catppuccin colors         30+ fish_color_* variables set to Mocha palette
     FZF_DEFAULT_OPTS          FZF themed to Catppuccin Mocha colors
-    Right prompt              fish_right_prompt: Docker context + timestamp
+    Right prompt              fish_right_prompt: exit code (on failure) + dim timestamp; always rendered
 
 The bang-bang system spans key_bindings.fish, abbr.fish, puffer.fish, and
 six expand_bang_*.fish functions. All are gated together — disabling C3
@@ -1694,6 +1694,34 @@ markers on the prompt line itself. This allows ov to use them as sticky
 section headers when browsing scrollback logs. Without Starship, fish's
 built-in prompt handles these markers automatically.
 
+### Catppuccin Fallback Prompt
+
+When Starship is absent or C3 overrides are disabled, a built-in nim-style
+two-line prompt activates from functions/fish_prompt.fish. No external
+dependencies — fish builtins only.
+
+Layout:
+
+    ┬─[user@host:~/path] (main)
+    ╰─>$
+
+Elements:
+
+    user        Yellow (Catppuccin Yellow); red if root
+    @host       Blue (local) or Teal (SSH)
+    ~/path      prompt_pwd abbreviation (Catppuccin Text)
+    (main)      Current git branch in Catppuccin Pink; omitted outside repos
+    ─[V:name]   Active Python venv basename; omitted when none
+    ─[N/I/R/V]  Vi-mode indicator when vi bindings are active
+    ┬─ / ╰─>    Connector lines: Catppuccin Green on success, Red on failure
+
+The right prompt (fish_right_prompt.fish) always renders, regardless of C3
+state. On failure it shows a red ✘ and the exit code; on success it shows
+only the dim timestamp:
+
+    ✘ 1   11:39:00     ← failed command
+    11:39:00           ← success (no ✘)
+
 ### FZF
 
 FZF is themed to Catppuccin Mocha via FZF_DEFAULT_OPTS set in