Require every track to name a track type and rework menu run flow

[vanlueckn]

Summary

• Breaking change: every track edge must now name a track type — there is no built-in type and no reserved "default" name. Modules that leave it out fail to compile with CompileError::MissingTrackType(<edge>), and the route editor's rule check reports the same before a run.
• Track types from other mods are dependencies like any other and must be named in depends:.
• The lay tool in the route editor arms itself with the first installed type, so newly drawn track carries one from the start.
• Consumers of track_type_at (audio roughness/reverb, precipitation reverb) now handle the Option explicitly instead of assuming a default.
• Docs updated (README, MODS.md, STATUS.md, screenshot skill) to describe the new requirement and the removed "default" name.

Testing

• Run cargo test --workspace — expecting 1136 tests green, including i18n key parity checks.
• Verify a mod line without track_type fails to compile with MissingTrackType.
• Verify the route editor rule check flags edges naming no type.
• Confirm the lay tool pre-assigns the first installed track type to new track sections.
• Check audio roughness/reverb and precipitation behavior on edges with and without assigned types.
• Screenshot pass of the route editor selection panel and map tinting: not run.