Add bun + pi-coding-agent + oh-my-pi to bootstrap; age encryption

Three parts:

1. .chezmoi.yaml.tmpl: reworked age config block
   - recipients moved under 'age:' key (correct structure per chezmoi docs)
   - identity: ~/.config/chezmoi/key.txt
   - recipients list with recovery key + miche per-machine key
   - recovery key pubkey: age1yyq42ctqwp5s5yd64week3aav9getk3p8aeyr5n5454d0v59a4dsjljsgs
   - miche pubkey: age1eja7trs8mmsgf0qga0h5fsdltaryxgk4ksumshar5xxtdx0exy3q0a5hc5
   - placeholders for byte/kaiser/rye/crouton (TODO: generate per-box keys
     and add when bootstrapping those boxes)

2. private_dot_omp/agent/: omp/oh-my-pi config from byte
   - config.yml (1.7KB) — model roles, fallback chains, theme, tools
   - mcp.json (351B) — firecrawl MCP server config
   - zai.key.age (540B) — zai-coding provider API key, age-encrypted to
     recovery + miche recipients. Decrypts to live ~/.omp/agent/zai.key
     on apply.

3. run_once_20: install bun + pi-coding-agent on both OSes
   - arch: bun from pacman (now in [extra])
   - debian: bun via curl-install to ~/.local (not in apt)
   - both: bun add -g @oh-my-pi/pi-coding-agent → omp binary in ~/.bun/bin
   - .zshrc.tmpl already adds ~/.bun/bin to PATH

To onboard a new box:
  1. ssh into the box
  2. age-keygen -o ~/.config/chezmoi/key.txt
  3. paste the public key into .chezmoi.yaml.tmpl recipients
  4. chezmoi age rekey   # rewrites *.age files to include new recipient
  5. commit + push
  6. chezmoi init --apply  # decrypts and writes zai.key live

private_dot_omp/agent/config.yml

@@ -0,0 +1,65 @@
+providers: 
+  webSearch: searxng
+searxng: 
+  endpoint: http://kaiser.local:8800
+symbolPreset: nerd
+theme: 
+  dark: dark-gruvbox
+  light: light
+setupVersion: 1
+modelRoles: 
+  default: minimax-code/MiniMax-M3:high
+  task: llama-swap.miche/qwen3.6-27b-mtp-rocmfp4-turbo
+  smol: llama-swap.miche/qwen3.6-35b-a3b-mtp-rocmfp4
+  plan: zai-coding/glm-5.2:xhigh
+  slow: minimax-code/MiniMax-M3:high
+  vision: llama-swap.miche/gemma4-12b
+retry: 
+  fallbackChains: 
+    default: 
+      - zai-coding/glm-5.2
+      - minimax-code/MiniMax-M3
+      - deepseek/deepseek-v4-pro
+      - llama-swap.miche/qwen3.6-27b-mtp-rocmfp4-turbo
+      - llama-swap.byte/qwen3.6-27b-mtp
+    task: 
+      - llama-swap.miche/qwen3.6-27b-mtp-rocmfp4-turbo
+      - llama-swap.byte/qwen3.6-27b-mtp
+      - zai-coding/glm-5.2
+      - minimax-code/MiniMax-M3
+    smol: 
+      - llama-swap.miche/qwen3.6-35b-a3b-mtp-rocmfp4
+      - llama-swap.byte/qwen3.6-35b-a3b-mtp
+      - llama-swap.miche/qwen3.6-27b-mtp-rocmfp4-turbo
+      - zai-coding/glm-5.2
+      - minimax-code/MiniMax-M3
+    plan: 
+      - zai-coding/glm-5.2:xhigh
+      - minimax-code/minimax-code:xhigh
+      - deepseek/deepseek-v4-pro:xhigh
+      - llama-swap.miche/step-3.7-flash:high
+    slow: 
+      - zai-coding/glm-5.2
+      - minimax-code/minimax-code
+      - deepseek/deepseek-v4-pro
+      - llama-swap.miche/step-3.7-flash
+    vision: 
+      - llama-swap.miche/gemma4-12b
+      - llama-swap.byte/gemma-4-12b-heretic
+      - llama-swap.miche/qwen3.6-27b-mtp-rocmfp4-turbo
+tools: 
+  approvalMode: yolo
+memory: 
+  backend: "off"
+github: 
+  enabled: true
+statusLine: 
+  preset: default
+  separator: powerline
+  transparent: true
+tui: 
+  textSizing: false
+defaultThinkingLevel: high
+personality: pragmatic
+hideThinkingBlock: true
+readLineNumbers: true