docs(configuration): Make env variables linkable via labels

why: LIBTMUX_SAFETY and other env vars should be cross-referenceable
from anywhere in the docs, following the pattern used by libtmux.
what:
- Restructure configuration.md: one heading per env var with MyST labels
  (LIBTMUX_SOCKET)=, (LIBTMUX_SOCKET_PATH)=, etc.
- {ref}`LIBTMUX_SAFETY` now links to configuration/#libtmux-safety
- Update safety page and glossary to use {ref} links

Author: tony

docs/configuration.md

@@ -6,12 +6,44 @@ Runtime configuration for the libtmux-mcp server. For MCP client setup, see {ref
 
 ## Environment variables
 
-| Variable | Type | Default | Description |
-|----------|------|---------|-------------|
-| `LIBTMUX_SOCKET` | string | (none) | tmux socket name (`-L`). Isolates the MCP server to a specific tmux socket. |
-| `LIBTMUX_SOCKET_PATH` | string | (none) | tmux socket path (`-S`). Alternative to socket name for custom socket locations. |
-| `LIBTMUX_TMUX_BIN` | string | `tmux` | Path to tmux binary. Useful for testing with different tmux versions. |
-| `LIBTMUX_SAFETY` | string | `mutating` | Safety tier: `readonly`, `mutating`, or `destructive`. See {ref}`safety`. |
+(LIBTMUX_SOCKET)=
+
+### `LIBTMUX_SOCKET`
+
+tmux socket name (`-L`). Isolates the MCP server to a specific tmux socket.
+
+- **Type:** string
+- **Default:** (none — uses the default tmux socket)
+
+(LIBTMUX_SOCKET_PATH)=
+
+### `LIBTMUX_SOCKET_PATH`
+
+tmux socket path (`-S`). Alternative to socket name for custom socket locations.
+
+- **Type:** string
+- **Default:** (none)
+
+(LIBTMUX_TMUX_BIN)=
+
+### `LIBTMUX_TMUX_BIN`
+
+Path to tmux binary. Useful for testing with different tmux versions.
+
+- **Type:** string
+- **Default:** `tmux`
+
+(LIBTMUX_SAFETY)=
+
+### `LIBTMUX_SAFETY`
+
+Safety tier controlling which tools are available. See {ref}`safety`.
+
+- **Type:** string
+- **Default:** `mutating`
+- **Values:** `readonly`, `mutating`, `destructive`
+
+## Setting environment variables
 
 Set environment variables in your MCP client config:
 
@@ -32,7 +64,7 @@ Set environment variables in your MCP client config:
 
 ## Socket isolation
 
-By default, the MCP server connects to the default tmux socket. Set `LIBTMUX_SOCKET` to isolate AI agent activity from your personal tmux sessions:
+By default, the MCP server connects to the default tmux socket. Set {ref}`LIBTMUX_SOCKET` to isolate AI agent activity from your personal tmux sessions:
 
 ```json
 "env": { "LIBTMUX_SOCKET": "ai_workspace" }
@@ -42,4 +74,4 @@ The agent will only see sessions on the `ai_workspace` socket, not your personal
 
 ## All tools accept `socket_name`
 
-Every tool accepts an optional `socket_name` parameter that overrides `LIBTMUX_SOCKET` for that call. This allows agents to work across multiple tmux servers in a single session.
+Every tool accepts an optional `socket_name` parameter that overrides {ref}`LIBTMUX_SOCKET` for that call. This allows agents to work across multiple tmux servers in a single session.

docs/glossary.md

@@ -29,7 +29,7 @@ Pane
     A tmux pane within a window. A pseudoterminal that runs a single process. Has an ID (e.g. `%1`) that is globally unique within a server.
 
 Safety tier
-    A level controlling which MCP tools are available: `readonly`, `mutating`, or `destructive`. Set via the `LIBTMUX_SAFETY` env var.
+    A level controlling which MCP tools are available: `readonly`, `mutating`, or `destructive`. Set via the {ref}`LIBTMUX_SAFETY` env var.
 
 Socket
     The Unix socket used to communicate with a tmux server. Can be specified by name (`-L`) or path (`-S`).

docs/topics/safety.md

@@ -14,7 +14,7 @@ libtmux-mcp uses a three-tier safety system to control which tools are available
 
 ## Configuration
 
-Set the safety tier via the `LIBTMUX_SAFETY` environment variable:
+Set the safety tier via the {ref}`LIBTMUX_SAFETY` environment variable:
 
 ```json
 {