feat(maestro): sidebar cards show diff stats and tool icons

Line 2 of a session card spelled out its blocked work ("1 uncommitted
file") and its command ("claude"). Both now render as marks: the
breakdown as diff notation, and the command's leading program as its
tool's icon in the web client.

The probe carries the line delta of the tracked changes — staged and
unstaged together, against HEAD — so `git add` never makes the counter
drop. Untracked files stay a file count; counting their lines means
reading every one off disk. A tracked change with no line delta falls
back to `~N` rather than claiming `+0 -0`.

The TUI keeps its command as text: a terminal cannot be assumed to have
a font carrying tool glyphs.

docs/SIDEBAR.md

@@ -37,7 +37,7 @@ itself is not.
 Line 2 reads left to right:
 
 ```
-<dot> [<duration>] [<detail>] [<blocked work> | exited] <command>
+<dot> [<duration>] [<detail>] [<diff stat> | exited] <command>
 ```
 
 Its minimum content is therefore the dot and the command.
@@ -64,12 +64,46 @@ truncates with `…` ahead of the trailing fragments — a long detail never
 pushes `<blocked work>`, `exited`, or `<command>` off the line, and neither
 client ever lets it wrap.
 
+`<diff stat>` is the blocked-work breakdown (#83) in diff notation, replacing
+the spelled-out `⚠ 3 uncommitted files, 2 unpushed commits`. It renders only
+while something would block an unforced kill, and reads:
+
+```
++<insertions> -<deletions> ?<untracked files> ↑<unpushed commits>
+```
+
+Each fragment is omitted when its count is zero. The line counts cover
+**tracked** changes only — staged and unstaged together, measured against
+`HEAD` — so a `git add` never makes the counter drop. Untracked files are
+counted as files, not lines: counting their lines means reading every one off
+disk, and `?3` already says what is there. A tree whose only tracked change
+carries no line delta — a mode change, a rename — shows `~<changed files>`
+instead of the additions and deletions, since `+0 -0` would describe it
+wrongly.
+
+Only `+` and `-` take colour (`--live` / `--danger` in the web client, the
+surface's `active` / `error` roles in the TUI); `~`, `?` and `↑` stay muted, so
+the fragment reads as a diff rather than as an alarm. The spelled-out phrasing
+of `maestro_protocol::InTheWay`'s `Display` does not disappear: it is the web
+card's tooltip and the wording of the kill refusal, so no two clients describe
+the same tree differently.
+
 `<command>` is unconditional and muted: the session's command line, shown on
 every card in both clients — no omission in the TUI, no name-vs-command
 comparison gating it. A session named by its command line then shows the same
 string on both lines; that is accepted, the price of a row that never changes
 height.
 
+In the **web client** the command's leading program is replaced by that tool's
+icon when it is one we have a mark for — Claude Code, Codex, opencode, Gemini
+CLI, Aider, Cursor, pi, and any shell — and only the remaining words of the
+command line follow as text. Recognition looks through a path, leading
+`FOO=bar` assignments and wrappers (`sudo`, `env`, `npx`, `pnpm dlx`, …); an
+unrecognised program keeps its full text, so the card never shows a mark
+standing for the wrong tool. The full command line stays in the card's tooltip
+either way. The **TUI** keeps the command as text: a terminal cannot be assumed
+to have a font carrying tool glyphs.
+
 ## Colour per activity state
 
 The state word is never spelled out — the colour carries it.
@@ -95,9 +129,10 @@ surface; a colour chosen for the card background is never painted onto the
 selection background. Contrast is a property of the palette (values are RGB)
 and is asserted in the palette's tests, not left to the terminal theme.
 
-The duration text inherits its state's colour; the blocked-work, exited and
-command fragments use the surface's `muted` role, since the ⚠ glyph already
-signals severity.
+The duration text inherits its state's colour; the exited and command
+fragments use the surface's `muted` role, as do the diff stat's `~`, `?` and
+`↑` fragments. Only `+` and `-` step outside the surface's muted role, and they
+take the `active` and `error` roles of the same surface.
 
 ## Duration format