chore: remove dead CI workflows (#5140)

* chore: remove dead CI workflows

12 workflows that target paths/apps that no longer exist or are stubs:

Broken (reference missing dirs):
- submit_flathub.yaml (no flatpak/ dir)
- mobile_bridge_ci.yaml (no apps/mobile/)
- extensions_cd.yaml (no extensions/)
- local_stt_e2e.yaml (no crates/cactus-sys/)
- cactus.yaml (no crates/cactus-sys/)

Hyprnote-era leftovers post-supernova:
- legacy_desktop_cd.yaml
- sign_passthrough.yaml (hyprnote-passthrough)
- download_staging.yaml (s3://hyprnote-build)
- desktop_publish.yaml (fastrepl/hyprnote2 Crabnebula app)

Empty stubs:
- ci.yaml (just 'echo pass', 86 noop runs in 2 weeks)
- bot_ci.yaml + bot_cd.yaml (apps/bot is just a .gitignore)

* fix: rustfmt api-support routes/mod.rs

Inline use axum::{Router, routing::post} — was breaking fmt CI on main.

* fix: drop apps/claw from Cargo.toml workspace members

Directory was deleted in #5139 but workspace member entry was left,
breaking cargo check / e2e / desktop_ci on every PR.

Author: ComputelessComputer