refactor: finish companion rename migration

Complete the remaining pi-to-companion rename across companion-os, web, vm-orchestrator, docker, and archived fixtures.

Verification:
- semantic rg sweeps for Pi/piConfig/getPi/.pi runtime references
- npm run check in apps/companion-os (fails in this worktree: biome not found)

Co-authored-by: Codex <noreply@openai.com>

packages/coding-agent/docs/rpc.md

@@ -2,12 +2,12 @@
 
 RPC mode enables headless operation of the coding agent via a JSON protocol over stdin/stdout. This is useful for embedding the agent in other applications, IDEs, or custom UIs.
 
-**Note for Node.js/TypeScript users**: If you're building a Node.js application, consider using `AgentSession` directly from `@mariozechner/pi-coding-agent` instead of spawning a subprocess. See [`src/core/agent-session.ts`](../src/core/agent-session.ts) for the API. For a subprocess-based TypeScript client, see [`src/modes/rpc/rpc-client.ts`](../src/modes/rpc/rpc-client.ts).
+**Note for Node.js/TypeScript users**: If you're building a Node.js application, consider using `AgentSession` directly from `@mariozechner/companion-coding-agent` instead of spawning a subprocess. See [`src/core/agent-session.ts`](../src/core/agent-session.ts) for the API. For a subprocess-based TypeScript client, see [`src/modes/rpc/rpc-client.ts`](../src/modes/rpc/rpc-client.ts).
 
 ## Starting RPC Mode
 
 ```bash
-pi --mode rpc [options]
+companion --mode rpc [options]
 ```
 
 Common options:
@@ -60,7 +60,7 @@ With images:
 
 If the agent is streaming and no `streamingBehavior` is specified, the command returns an error.
 
-**Extension commands**: If the message is an extension command (e.g., `/mycommand`), it executes immediately even during streaming. Extension commands manage their own LLM interaction via `pi.sendMessage()`.
+**Extension commands**: If the message is an extension command (e.g., `/mycommand`), it executes immediately even during streaming. Extension commands manage their own LLM interaction via `companion.sendMessage()`.
 
 **Input expansion**: Skill commands (`/skill:name`) and prompt templates (`/template`) are expanded before sending/queueing.
 
@@ -503,7 +503,7 @@ If output was truncated, includes `fullOutputPath`:
     "exitCode": 0,
     "cancelled": false,
     "truncated": true,
-    "fullOutputPath": "/tmp/pi-bash-abc123.log"
+    "fullOutputPath": "/tmp/companion-bash-abc123.log"
   }
 }
 ```
@@ -752,21 +752,21 @@ Response:
         "name": "session-name",
         "description": "Set or clear session name",
         "source": "extension",
-        "path": "/home/user/.pi/agent/extensions/session.ts"
+        "path": "/home/user/.companion/agent/extensions/session.ts"
       },
       {
         "name": "fix-tests",
         "description": "Fix failing tests",
         "source": "prompt",
         "location": "project",
-        "path": "/home/user/myproject/.pi/agent/prompts/fix-tests.md"
+        "path": "/home/user/myproject/.companion/agent/prompts/fix-tests.md"
       },
       {
         "name": "skill:brave-search",
         "description": "Web search via Brave API",
         "source": "skill",
         "location": "user",
-        "path": "/home/user/.pi/agent/skills/brave-search/SKILL.md"
+        "path": "/home/user/.companion/agent/skills/brave-search/SKILL.md"
       }
     ]
   }
@@ -778,12 +778,12 @@ Each command has:
 - `name`: Command name (invoke with `/name`)
 - `description`: Human-readable description (optional for extension commands)
 - `source`: What kind of command:
-  - `"extension"`: Registered via `pi.registerCommand()` in an extension
+  - `"extension"`: Registered via `companion.registerCommand()` in an extension
   - `"prompt"`: Loaded from a prompt template `.md` file
   - `"skill"`: Loaded from a skill directory (name is prefixed with `skill:`)
 - `location`: Where it was loaded from (optional, not present for extensions):
-  - `"user"`: User-level (`~/.pi/agent/`)
-  - `"project"`: Project-level (`./.pi/agent/`)
+  - `"user"`: User-level (`~/.companion/agent/`)
+  - `"project"`: Project-level (`./.companion/agent/`)
   - `"path"`: Explicit path via CLI or settings
 - `path`: Absolute file path to the command source (optional)
 
@@ -1173,7 +1173,7 @@ Set the terminal window/tab title. Fire-and-forget.
   "type": "extension_ui_request",
   "id": "uuid-8",
   "method": "setTitle",
-  "title": "pi - my project"
+  "title": "companion - my project"
 }
 ```
 
@@ -1372,7 +1372,7 @@ import subprocess
 import json
 
 proc = subprocess.Popen(
-    ["pi", "--mode", "rpc", "--no-session"],
+    ["companion", "--mode", "rpc", "--no-session"],
     stdin=subprocess.PIPE,
     stdout=subprocess.PIPE,
     text=True
@@ -1411,7 +1411,7 @@ For a complete example of handling the extension UI protocol, see [`examples/rpc
 const { spawn } = require("child_process");
 const readline = require("readline");
 
-const agent = spawn("pi", ["--mode", "rpc", "--no-session"]);
+const agent = spawn("companion", ["--mode", "rpc", "--no-session"]);
 
 readline.createInterface({ input: agent.stdout }).on("line", (line) => {
   const event = JSON.parse(line);