Cas/reset evolve state on dirchange ENG-441

[Cas Linden (CasLinden)]

Summary

• Recompute step and evolve state from actual git status of the new config dir
• Return SetDirResult { dir, evolveState?, hosts? } from config_set_dir / config_pick_dir — frontend applies evolve state and host list immediately without extra round trips
• Restart watcher + seed git status to fix git repo error propagation and missed flake detections
• Browse picker now opens at parent of dir, not inside it
• Host list unaffected when same dir is picked

• BootstrapConfig detects whether flake.nix exists and whether the repo has any commits — offers "Make initial commit" instead of failing when a flake is present but uncommitted
• bootstrap_default_config handles existing flake.nix — commits it in place rather than returning "directory is not empty"
• After committing an existing single-host flake, that host is auto-selected
• Bootstrap errors displayed inline below the button (not via global error banner, which the watcher can clobber)
• Global error banner suppressed entirely on the setup step
• Directory picker submits on Enter and only blurs if validation succeeds

Test Plan

• Remove config dir → setup step; pick a dir with a valid flake → host selector shows (not bootstrap)
• Change config dir in settings → watcher switches immediately, evolve state resets
• Same dir re-selected → no state change
• Browse opens at parent of currently selected dir
• Cancelling Browse leaves state unchanged

• Pick a dir with flake.nix and no git commits → "Make initial commit" button shown (not "Create Default Configuration")
• Click "Make initial commit" → commit created, host auto-selected if flake has exactly one darwinConfiguration
• Pick an empty dir → "Create Default Configuration" with hostname input shown
• Pick a non-empty dir without flake.nix → bootstrap shows "Create Default Configuration" (not commit variant)
• Bootstrap fails (e.g. non-empty dir without flake) → error shown inline below button, clears when a new dir is selected
• Type a path in the directory input and press Enter → validates and blurs on success, stays focused on error

[github-actions]

	Warnings
⚠️	Please assign this PR to someone (usually yourself).

📋 PR Overview

Lines changed	368 (+241 / -127)
Files	0 added, 12 modified, 0 deleted
Draft / WIP	no
Has Test Plan	yes
New UI components	no
New Storybook stories	no
New Rust modules	no
New TS source files	no
New tests	no
package.json touched	no
Cargo.toml touched	no
Infra / CI touched	no

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