feat(ui): make the toolbar icon size configurable

Follow-up to item 56. With the toolbar now following the desktop's
button style, an "icon only" desktop makes the icon the whole control,
and this style reports PM_ToolBarIconSize as 16px, which is a small
target for a button with no text beside it.

A [general] toolbar_icon_size key, 16 to 64, defaulting to 24 rather
than to the style's own metric. Setting it to 16 restores the theme's
value.

Clamped and reported, unlike message_zoom, which documents a 0.5 to 3.0
range in the README and enforces none of it. Both ends here break the
UI that would be used to fix them: too small is an invisible icon, too
large is a toolbar taller than the window.

The unenforced message_zoom range is recorded as item 58 rather than
fixed here, since it is a separate defect that predates this change.

Also documents in the README that saved-query button labels are the key
names from the user's own [queries] section, which is why the "Flagged"
button still read that way after the action was renamed: it is a user's
query name, not a string this code owns. The sample config now shows
`Important = tag:flagged` to teach the wording the UI uses.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

1 files changed, 34 insertions, 0 deletions

diff --git a/docs/superpowers/plans/2026-08-03-post-0.1.0-usability.md b/docs/superpowers/plans/2026-08-03-post-0.1.0-usability.md
index 52cc023..ba0ade5 100644
--- a/docs/superpowers/plans/2026-08-03-post-0.1.0-usability.md
+++ b/docs/superpowers/plans/2026-08-03-post-0.1.0-usability.md
@@ -115,6 +115,7 @@ taking that too literally.
 | 55 | In a narrow window the message pane is invisible | presentation | XS | open |
 | 56 | No action carries an icon, so the toolbar reserves space for nothing | presentation | S | **done** |
 | 57 | "Flag" would read better as "Important" or "Starred" | presentation | XS | **done** |
+| 58 | `message_zoom` documents a 0.5 to 3.0 range and enforces none of it | correctness | XS | open |
 
 Sizes are rough: XS under an hour, S a sitting, M a session.
 
@@ -3542,6 +3543,39 @@ guard proving the thread did not already carry it. Mutating the tag to
 `important` fails it, and also fails two pre-existing held-edit tests, which is
 independent confirmation that `flagged` is load-bearing across the suite.
 
+## 58. `message_zoom` documents a 0.5 to 3.0 range and enforces none of it
+
+**Observed:** not by the user. Found on 2026-08-09 while adding
+`toolbar_icon_size`, by reading `message_zoom` as the model for a bounded
+numeric key and noticing it is not bounded.
+
+**Cause, verified in code.** `src/config.cpp:79-90` parses the value with
+`toDouble()` and assigns it on success. The parse failure is reported, but
+nothing checks the range. The README documents "0.5 to 3.0" (`README.md`, the
+`[general]` block), and `m_messageZoom` is never clamped anywhere else:
+`src/mainwindow.cpp:145` passes it straight to the saved-state default.
+
+So `message_zoom = 500` is accepted and applied. Unlike the toolbar icon size,
+this one is recoverable, since the zoom is adjustable from the UI and the
+adjusted value is what gets saved, but the first render is unusable.
+
+**Approach.** Clamp with a report, exactly as `toolbar_icon_size` does
+(`src/config.cpp`, the `kMinToolbarIconSize`/`kMaxToolbarIconSize` block). Both
+ends already have documented bounds, so this is applying the README's own
+numbers.
+
+**Constraints.**
+
+- Report rather than silently clamp. Silence is how this went unnoticed: the
+  key parses, so nothing ever said the value was not being honoured.
+- Do not extend this to `mark_read_delay_ms`, whose zero and negative values are
+  meaningful and deliberately unclamped (`src/config.cpp:96-102`).
+
+**Verification.** `test_config` already has the pattern in
+`toolbarIconSizeIsClampedAndReported`; mirror it. Note that
+`messageZoomDefaultsAndValidates` exists and passes today, so it is asserting
+only on the parse and not on the range.
+
 ## Deferred, unsized, or split out
 
 Items noted while triaging but not part of the original list. Same numbering