Reduce duplication, fix compile errors, harden tests

[paddo]

Summary

• Extract sha256_hex() utility replacing 34 duplicate inline calls across 9 files
• Extract App::spawn_sync() (5 sites) and App::reload_state() (9 sites) in dashboard
• Consolidate 4 identical confirm popup renders into single render_confirm_popup()
• Remove redundant App::syncing bool (was always sync_child.is_some())
• Fix known_profile_names() calling Config::load() from disk on every render pass
• Add DEFAULT_PROFILE constant replacing scattered "dev" string literals
• Add missing add_profile_dotfile / remove_profile_dotfile functions (compile fix)
• Add installing parameter to status bar render (compile fix)
• Fix matches!() without assert!() in secret scanner tests (type checks were no-ops)
• Add tests for sha256_hex, canonical_project_file_path path traversal rejection
• Tighten weak/fragile test assertions

Net: -77 lines across 18 files. 214 tests pass, zero clippy warnings.

Test plan

• cargo clippy --all-targets -- -D warnings passes
• cargo test -- --include-ignored — 214 tests pass
• cargo build succeeds (previously had 3 compile errors)

[paddo]

/songify

[diffbeats]

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"Reduce duplication, fix compile errors, harden tests"

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Lyrics

[Verse]
Thirty-four shas, a tangled mess
Nine files now feel less stressed
Spawn sync and reload, a refactor's quest
Confirm popups, finally blessed

[Chorus]
Seventy-seven lines, a mighty feat,
Two hundred fourteen tests, can't be beat
Clippy's silent, the compiler's sweet,
Our code's now clean, can't be beat!

[Verse 2]
"Dev" strings got a brand new name,
Dotfiles fixed, it's not a game
Installing status, no more shame
Tests are stronger, winning the fame

[Chorus]
Seventy-seven lines, a mighty feat,
Two hundred fourteen tests, can't be beat
Clippy's silent, the compiler's sweet,
Our code's now clean, can't be beat!