Ground inspection in a chosen claude session (#11, #12)

[samkeen]

Pivot the inspector from "knobs.cc's own CWD" to a session it picks from the running process table. Closes the longstanding paradox where the project / project_local rail rows showed knobs.cc's launch directory rather than the user's claude session, and the cli row sat permanently empty because flags couldn't be observed without reading another process's argv.

New surface:

• read_runtime_layer Tauri command enumerates same-UID claude / claude-code processes via the sysinfo crate and returns each one's cwd, argv, and environ.
• read_settings_layers grows attached_pid / project_root_override args. The new ProjectSource enum routes the three grounding modes (Attached / Picked / CurrentDir-fallback) through one snapshot read.
• cli_layer.rs parses argv against catalog/cli-settings-map.json (5 starter flags: --model, --permission-mode, --effort, --agent, --add-dir) and emits a real cli LayerRead.
• env_layer.rs grows read_env_layer_attached(environ), so the env precedence layer reads the attached claude's environ when attached rather than knobs.cc's own.
• SessionPill in the topbar drives a four-state picker (loading / 0 / 1 / 2+ claudes, plus unsupported on Windows). Single-process case auto-attaches; multi-process opens an inline picker; zero drops to a native folder picker via the dialog plugin.
• EnvVarsPanel gains an attached column alongside shell, a per-row Δ badge when the two diverge, and attached / Δ diff filter chips that appear only when attached.

Capability surface gains one grant: dialog:allow-open for the project-directory fallback picker. Cross-process reads stay Rust-only (no JS-side process/fs plugin grants). The "no fs, shell, process, updater" rule from design-notes.md still holds.

Other refinements during smoke-testing:

• MERGED chip on array-merge paths now only fires when 2+ layers actually contributed elements. Single-contributor array paths render as normal set rows with the contributor's badge; the per-element drawer view still renders.
• #[tauri::command(rename_all = "snake_case")] on read_settings_layers — Tauri 2 defaults to camelCase command args while this project's wire format is snake_case throughout; without the override attached_pid from JS silently deserialized to None.
• The repo's "Claude Code reads dotenv files at startup" claim (footnote, four spec spots, Read another running claude process's argv + env (the "runtime introspection" layer) #11 body) was wrong. Smoke-tested with claude -p reading a .env-only var: nothing. The claim is removed.

Docs sweep: user-facing copy (README, HelpView, EnvVarsPanel footnote, waterfall empty-state) describes grounded inspection as the product without narrating the pivot. Spec docs (attach-mode.md, inspector-ui, design-notes, settings-display, roadmap) reference the implementation contract in attach-mode.md and the closed issues.

Small code-cleanup items (dedup set_dotted_path between cli + env layer, strip pivot/legacy framing from comments, two missing test cases) parked in issue #14.