Add sidebar metadata CLI subcommands and API docs (#305)

* Add sidebar metadata CLI subcommands and API docs

Expose set-status, clear-status, list-status, set-progress,
clear-progress, log, clear-log, list-log, and sidebar-state as
proper CLI subcommands with --help support and usage() listing.
Previously these only existed as raw socket commands.

Also adds a "Sidebar metadata commands" section to the docs site
API reference page.

* Quote multi-word values in socket command strings

Fix set-progress --label and log message forwarding to properly
quote values before sending to the socket tokenizer. Without
quoting, multi-word labels like "Build step one" would be split
into separate tokens. Also quote --source values for consistency.

* Fix socket quoting: escape backslashes and quote status values

Add socketQuote() helper that escapes both backslashes and double
quotes before wrapping in quotes. Apply it to:
- set-status value (prevents --flags in values being parsed as options)
- set-status --icon and --color values
- set-progress --label
- log --source and message text

Fixes values like "pytest --maxfail=1" or "C:\new\build" being
mangled by the socket tokenizer.

* Escape newlines in socketQuote to prevent socket framing breakage

The socket protocol uses newline as message terminator, so embedded
newlines/carriage returns in values would truncate the command.

* Parse flags before positionals in set-status, clear-status, set-progress

Fixes flags-first invocation like `cmux set-status --workspace workspace:2
build compiling` which previously grabbed `--workspace` as the key.
Now all flags are extracted first, then positional args are validated.

web/app/docs/api/page.tsx

@@ -5,7 +5,7 @@ import { Callout } from "../../components/callout";
 export const metadata: Metadata = {
   title: "API Reference",
   description:
-    "cmux CLI and Unix socket API reference. Workspace management, split panes, input control, notifications, environment variables, and detection methods.",
+    "cmux CLI and Unix socket API reference. Workspace management, split panes, input control, notifications, sidebar metadata (status, progress, logs), environment variables, and detection methods.",
 };
 
 function Cmd({
@@ -281,6 +281,74 @@ cmux list-notifications --json`}
         socket={`{"id":"notif-clear","method":"notification.clear","params":{}}`}
       />
 
+      <h2>Sidebar metadata commands</h2>
+      <p>
+        Set status pills, progress bars, and log entries in the sidebar for any
+        workspace. Useful for build scripts, CI integrations, and AI coding
+        agents that want to surface state at a glance.
+      </p>
+
+      <Cmd
+        name="set-status"
+        desc="Set a sidebar status pill. Use a unique key so different tools can manage their own entries."
+        cli={`cmux set-status build "compiling" --icon hammer --color "#ff9500"
+cmux set-status deploy "v1.2.3" --workspace workspace:2`}
+        socket={`set_status build compiling --icon=hammer --color=#ff9500 --tab=<workspace-uuid>`}
+      />
+      <Cmd
+        name="clear-status"
+        desc="Remove a sidebar status entry by key."
+        cli={`cmux clear-status build`}
+        socket={`clear_status build --tab=<workspace-uuid>`}
+      />
+      <Cmd
+        name="list-status"
+        desc="List all sidebar status entries for a workspace."
+        cli={`cmux list-status`}
+        socket={`list_status --tab=<workspace-uuid>`}
+      />
+      <Cmd
+        name="set-progress"
+        desc="Set a progress bar in the sidebar (0.0 to 1.0)."
+        cli={`cmux set-progress 0.5 --label "Building..."
+cmux set-progress 1.0 --label "Done"`}
+        socket={`set_progress 0.5 --label=Building... --tab=<workspace-uuid>`}
+      />
+      <Cmd
+        name="clear-progress"
+        desc="Clear the sidebar progress bar."
+        cli={`cmux clear-progress`}
+        socket={`clear_progress --tab=<workspace-uuid>`}
+      />
+      <Cmd
+        name="log"
+        desc="Append a log entry to the sidebar. Levels: info, progress, success, warning, error."
+        cli={`cmux log "Build started"
+cmux log --level error --source build "Compilation failed"
+cmux log --level success -- "All 42 tests passed"`}
+        socket={`log --level=error --source=build --tab=<workspace-uuid> -- Compilation failed`}
+      />
+      <Cmd
+        name="clear-log"
+        desc="Clear all sidebar log entries."
+        cli={`cmux clear-log`}
+        socket={`clear_log --tab=<workspace-uuid>`}
+      />
+      <Cmd
+        name="list-log"
+        desc="List sidebar log entries."
+        cli={`cmux list-log
+cmux list-log --limit 5`}
+        socket={`list_log --limit=5 --tab=<workspace-uuid>`}
+      />
+      <Cmd
+        name="sidebar-state"
+        desc="Dump all sidebar metadata (cwd, git branch, ports, status, progress, logs)."
+        cli={`cmux sidebar-state
+cmux sidebar-state --workspace workspace:2`}
+        socket={`sidebar_state --tab=<workspace-uuid>`}
+      />
+
       <h2>Utility commands</h2>
 
       <Cmd