v0.5.5

**Refreshed icons, and what users asked for.** IngeTrazo keeps only free
pieces: the link to an external `.skp` converter and the `.skp` export are
retired, and `.skp` files keep opening with the built-in free reader. The
icons are updated to stay consistent across the interface. And a batch of fixed reports: the orbit turns about what you
are looking at, Push/Pull stops at the Tape Measure's guides, rotating lands
exactly on the snapped point, saving no longer leaves a phantom «unsaved
changes», and lengths show in the document's units.

### Removed
- **The link to an external `.skp` converter.** It was never part of
  IngeTrazo: no package included it, and IngeTrazo only offered to download
  it separately to run under Wine. That link and the download are gone.
  `.skp` files open with the built-in free reader (OpenSKP); when one cannot
  be read, IngeTrazo says so and suggests exporting it as COLLADA or OBJ from
  the program it came from.
- **Export to `.skp`**: the blank template the writer used is no longer
  shipped in any package (PyInstaller, Flatpak, Snap), and `--check` fails a
  package that still carries it. To take a model to another program, export
  COLLADA (.dae), OBJ or glTF.
- The tests and the validation tool that depended on that converter;
  `scripts/skp_diff.py` now compares against a reference `.dae`.
- **Help ▸ Get more models** links to Poly Haven, ambientCG and Sketchfab.

### Changed
- **Icons updated to stay consistent with the rest of the interface**:
  Walk is two footprints, Look Around a head seen
  from above with its cone of vision, the solid tools two overlapping discs,
  text a T in a frame, Zoom Extents four corners around the magnifier, and
  dimensions end in dots. **Position Camera is a small camera** with an
  orange lens and a mark below, and **the Eraser a tilted rubber** with an
  orange tip. The **standard views are still the little house** with the
  viewed wall in orange.
- **IngeTrazo presents itself on its own terms**: the README, the Flatpak and
  the Snap listings describe it with its motto, *draw as if by hand*, and say
  how its name is pronounced (in-je-TRA-so: *inge*niería + *trazo*,
  suggested by @pacaeiro).

### Added
- **Repeat the last command with Shift+R**, also as the first entry of the
  right-click menu (#145, @canalsecuario-blip).

### Fixed
- **Rotate and the Protractor snap to the red axis even when the reference
  line is a few degrees off it** (#140, @pacaeiro). The arm stuck to the
  reference's own direction («Through point») and the extension of other
  edges moved the angle with the cursor's distance. The protractor's arm no
  longer uses the line-drawing inferences (through point, extension, from
  point): only points and axes.
- **The extension no longer comes out of a circle, arc or smoothed-surface
  segment, nor out of a hidden edge** (#140): it drew dashed lines across the
  sphere.
- **The orbit turns about what you are looking at** (#164, @mariuseng-dot):
  the point of the model under the cursor when the drag starts, or the model
  in view if you point at the sky, and that point stays under the cursor.
  It used to turn about the camera's target, very far away in a large model.
- **Push/Pull stops at the Tape Measure's guide points and lines** (#165,
  @ewertondiaseng-byte), with the «Guide point» / «On line» hint.
- **Rotate lands exactly on the snapped point** (#163, @fafecm): with the
  second click snapped to a point, the label's angle rounded to 0.1° was
  applied (−70.3°) and the edge ended ~0.7 mm off at 2 m from the pivot. The
  preview no longer accumulates error either: it is always computed from a
  copy taken at the start, and cancelling leaves everything identical.
- **Saving and closing no longer asks about unsaved changes** (#159,
  @pacaeiro): any selection change after saving counted as a modification.
- **Circle, Polygon, Fillet and Follow Me show measurements in the
  document's units** (#149, @xyont): in millimetres they said metres. What
  you type in the value box shows the unit it will be read in, and
  «sides»/«segments» are translated.
- **The Rectangle takes `200,100`** (no space) as width and height (#152,
  @xyont). `200, 100` and `200;100` still work; in the other tools the comma
  is still the decimal separator.
- **A reversed face stays reversed as you keep drawing** (#144,
  @canalsecuario-blip).
- **Every tab of the right tray fits in the 240 px minimum** (#139,
  @felixriestra): the Layers buttons and the Terrain combos were cut off.