feat: use the application iconfeature/qaction-menus

The icon was committed in a previous session and referenced nowhere: no
qrc, no .desktop entry, no setWindowIcon. It is wired up now, as a window
icon, a desktop entry, and install rules placing both into hicolor and
share/applications.

resources.qrc belongs to the executable rather than to qtmaildir_lib. A
qrc compiled into a static library registers itself from a global
initialiser, and the linker discards that object because nothing
references it: the build succeeded, qInitResources_resources() was
present in the .a, and QFile::exists(":/icons/qtmaildir.svg") still
returned false at runtime. Verified loading at 16, 32 and 64 pixels after
the move.

Toolbar and menu actions take icons from the system theme by their
standard names, so they match the rest of the desktop rather than
shipping bespoke art. A theme lacking one leaves that action as text,
which still works.

1 files changed, 39 insertions, 1 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 1e08bb1..915c8cb 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
@@ -44,8 +44,9 @@ taking that too literally.
 | 8 | No buttons or menu entries for archive, undo, etc | discoverability | M | **done** |
 | 9 | No in-app view of configured shortcuts | discoverability | S | **done** |
 | 10 | Reaching an account's inbox takes two steps | workflow | S | open |
-| 11 | Icon, `.desktop` file, SlackBuild | packaging | M | open |
+| 11 | Icon, `.desktop` file, SlackBuild | packaging | M | **partly done**: icon and `.desktop` landed, SlackBuild open |
 | 13 | No visual feedback that an action stuck | feedback | S | **done** |
+| 14 | Tag column unreadable, tags need another home | presentation | M | **done** |
 
 Sizes are rough: XS under an hour, S a sitting, M a session.
 
@@ -398,6 +399,43 @@ and inspected: normal, unread, deleted, spam, and deleted-plus-unread rows.
 
 ---
 
+## 14. Tag column unreadable
+
+**Observed:** with tags spelled out per row the column ran to 500 pixels of
+mostly repeated text ("account-privateemail-danilo.macri attachment flagged
+inbox passed replied"), dominated by the account prefix, and consumed most of
+the list's width.
+
+**Cause:** presentation, not data. 96 tags in this database, many hierarchical
+(`shopping/amazon`, `mailing-list/SBo`), rendered as a joined string.
+
+**Approach:** the column is gone. Tags now render as coloured chips in two
+places, split by taxonomy:
+
+- The **account tag** says which mailbox a thread came from. It draws as a chip
+  in front of the subject, coloured and labelled from its own `[account.<key>]`
+  stanza via new `color` and `label` keys. `label` is display-only; the notmuch
+  tag is never renamed.
+- **Functional tags** say what state a thread is in. They fill a single row
+  under the message pane, with overflow collapsing into a `+N` chip whose
+  tooltip lists the hidden ones. A single row keeps the message area from
+  shifting between threads with different tag counts.
+
+Colours resolve exact tag first, then top-level prefix, so one `shopping` entry
+covers the hierarchy without listing all 96. Unconfigured tags fall back to a
+hash of the name, stable so a chip never changes colour as the list scrolls.
+
+**Defect found while building:** QSettings treats `/` in a key as a group
+separator, so `shopping/amazon` becomes a nested key that `childKeys()` never
+returns. Reading `[tagcolors]` with `childKeys()` silently dropped every
+hierarchical tag, and each fell through to its prefix colour. Fixed by reading
+`allKeys()`, with a regression test. The same gotcha is already documented in
+`CLAUDE.md` for `[account.work]` section names.
+
+**Deferred:** clicking a chip to search that tag. Display only for now.
+
+---
+
 ## Deferred, unsized, or split out
 
 Items noted while triaging but not part of the original list. Same numbering