feat(ui): reset a whole tab from its icon's context menu

[s6stkurz]

What this does

Right-click a tab icon in the right panel for Reset Setup to Defaults — every panel on that
tab returns to its defaults in one commit, and one Ctrl+Z walks the whole thing back.

Clearing Setup today means resetting Calibration, Demosaic, Normalization and Roll Analysis from
four separate panel headers, and undoing that costs four presses. The per-panel header resets are
unchanged; this is a second way in, for when the whole tab is what you want gone.

The five workflow tabs offer it: Setup, Geometry, Exposure, Lab & Toning, Finish.

• Favorites and History hold no settings.
• Export is mirrored into sticky settings that reach frames other than the one in front of
  you, and ExportConfig carries machine paths — a reset would re-point the destination for the
  session.
• Metadata is archival content (capture date, GPS, roll and frame), not settings.
  MetadataConfig() wholesale would be a deletion wearing a reset's label, and the panel already
  has per-group clears with the right verb.
• Scan drives the scanner and camera through global device settings, so a reset there would
  not be part of the frame's edit and would not be undoable.

None of those five gets a menu at all, rather than a menu with a dead row.

The item is shown and greyed when the tab is already at its defaults, matching the canvas
right-click menu. Whether it is enabled is read from the same fold the reset commits, not from
the modified counts, which trail a 150 ms debounce.

The part that needs your agreement

An aggregate reset has to produce one WorkspaceConfig and one update_config call, or the tab
costs N undo steps. The 14 per-panel resets existed only as lambdas in _connect_signals with
three different commit routes, so there was nothing to compose.

So what each panel owns now lives in one table, _SECTION_RESETS, that both the header reset and
the tab reset fold. That collapses SessionManager.reset_section,
AppController.clear_roll_baseline and four ControlsPanel helpers into it — a net deletion, but
it does touch working code. Two consequences worth your eyes:

1. Every panel reset now commits through apply_config. It compares source_token and
   re-decodes when a reset moves a source input. Previously only the two source-baking helpers
   did this, so a Normalization reset that cleared linear_raw rendered the stale decode. That is
   fixed as a side effect rather than on purpose; say the word if you would rather see it on its
   own.
2. Normalization still resets the whole ProcessConfig, as it does today, which also
   defaults the Calibration, Demosaic and Roll Analysis fields that live on it. I kept the
   existing behaviour rather than scoping it, because scoping is a visible change to a control
   that is not what this PR is about. It costs nothing here: a whole-config reset subsumes the
   three scoped siblings, so the Setup fold is order-independent either way.

If you would rather not take the refactor, I can rework this as additive code that leaves the 14
wirings alone — it duplicates the "what does Calibration own" knowledge, which is why I did not
lead with it.

Testing

tests/test_tab_reset.py, 16 tests over three layers:

• the fold — a tab reset defaults every panel on it and nothing off it, a panel reset stays inside
  its own panel, the fold is identity on a clean tab, a roll reset drops the cached per-frame
  bounds and a lock_bounds frame keeps them
• the commit — one apply_config for a whole tab, none for a clean one, and Dodge & Burn drops
  its mask selection
• the menu — against the real tab strip, so the five workflow tabs produce their labels and the
  other five produce no menu; plus the greying, the trigger, and the keyboard route

test_clear_roll_baseline_resets_axes moved out of tests/test_controller.py with its subject.

make format, make lint, make type clean; full suite passes. One unrelated failure on my
machine, test_metadata_presets.py::test_load_tooltip_follows_a_rebinding, expects Ctrl+Shift+L
where macOS renders ⇧⌘L — it fails the same way on main with this branch stashed, and CI runs
Ubuntu.

Notes

• reset_tab is registered with no default key: every Ctrl+<digit> is a tab already. One entry
  rather than five, since five unbound rows in the ? overlay for one concept reads badly. Bound
  by hand it takes the tab on screen, where the menu takes the tab under the pointer.
• A tab spilled into the » overflow menu cannot be right-clicked — the spilled items are
  QActions. The bar pins the active tab, so selecting a tab first always brings its button back.
  I left build_overflow_menu alone rather than grow it a submenu here.
• Filtration is hidden in B&W mode but is still reset by an Exposure-tab reset. Its fields are
  part of the edit and inert in that mode.
• docs/USER_GUIDE.md gains two sentences on the existing panel-header line. No new
  <!-- panel: --> marker, and docs/CHANGELOG.md is untouched.

There is no open issue for this one, so it arrives unsolicited. Happy to close it, split it, or
rework it if this is not a direction you want.

🤖 Generated with Claude Code