feat(computer-use): TuriX-CUA inspired Interactive-View workflow + accuracy hardening

[bobleer]

Summary

Inspired by the TuriX-CUA open-source project, this PR overhauls BitFun's desktop Computer Use stack on macOS so the agent can reliably see → plan → act → verify on real GUIs (Tauri WebViews, Cocoa apps, mini-apps embedded in BitFun itself).

The previous AX-only / coordinate-clicking flow had two systemic failure modes:

1. The model couldn't tell which on-screen widget to act on (no labelled overlay), so it kept clicking the wrong region.
2. Even when it picked the right widget, the click often didn't land — AX press not supported, view changed between observation and action, no fallback path.

What's in this PR

Interactive-View pipeline (S1-S4)

• New types in bitfun-core: AxNode → InteractiveElement → InteractiveView (with stable i index, role/label, image-pixel + screen geometry, optimistic-locking digest).
• interactive_filter.rs — turns the raw macOS AX dump into a clean, indexed, deduplicated list of actionable elements.
• som_overlay.rs — Set-of-Mark JPEG overlay that renders numbered bounding boxes on top of a focused-window screenshot (drop-in for the agent's vision).
• desktop_host.rs — wires the above into build_interactive_view, on top of the new macos_ax_dump.

ControlHub desktop actions (S5)

Four new actions exposed via ControlHub, all addressed by a single i index plus a before_view_digest:

• interactive_click (with click count, modifiers, mouse button)
• interactive_type_text (focus an element by i, then type)
• interactive_scroll
• interactive_key_chord

Click reliability hardening

• Digest stability: compute_interactive_view_digest now hashes only role + bucketed geometry; ignores transient focus/value/label jitter, so harmless re-renders no longer invalidate the view.
• Auto-rebuild on STALE: interactive_click catches STALE_INTERACTIVE_VIEW, rebuilds the view once, retries with the new digest, and tags the result with auto_rebuilt_view_after_stale so the agent knows to re-verify.
• Multi-channel fallback: AX press → image-pixel pointer click. If the AX path fails (widget not in AX tree, AXPress not supported, etc.), we fall back to app_click { target: ImageXy } at the element's image-pixel center; result is tagged fallback_image_xy.
• Relaxed click_element validation: text_contains and node_idx are now valid lone locators (previously you had to also pass title_contains/role_substring/identifier_contains).

UI consolidation

• Card-merging heuristic in interactive_filter: when an actionable container (AXCell, AXRow, AXButton, AXLink, AXGroup, …) fully contains smaller actionable children and is ≥1.5× their area, the children are absorbed. This dramatically cuts overlay clutter on real apps (table rows, list items, card grids).

Prompt update (claw_mode.md)

• Replaces the old AX-first guidance with Interactive-View-first workflow.
• Adds a mandatory OBSERVE → PLAN → EXPECT → VERIFY loop template the agent must follow on every interactive_* turn (single biggest accuracy lever in our internal tests).
• Documents the new auto_rebuilt_view_after_stale / fallback_image_xy recovery notes and how to react to them.

Supporting macOS plumbing

• macos_ax_dump.rs — non-throwing AX tree snapshot with cached AXUIElementRef lookup by node idx.
• macos_ax_write.rs — safe AXPress wrapper (@try/@catch) returning structured AxWriteOutcome.
• macos_bg_input.rs — background CGEvent-based mouse / scroll / keyboard / typing into a target pid (no cursor hijack).
• macos_list_apps.rs — running app enumeration.
• Plus recursion_limit = "256" for the new generic-heavy modules.

Test plan

• cargo check -p bitfun-desktop -p bitfun-core — clean.
• Unit tests: interactive_filter (incl. new card_container_absorbs_contained_actionable_children), desktop_host digest helpers.
• Manual dogfooding on macOS: opening the BitFun "五子棋" mini-app via interactive_click, typing into search fields via interactive_type_text, scrolling lists via interactive_scroll — all succeed without falling back to coordinate guessing.
• Reviewer dogfooding on a fresh macOS install (please flag any AX-permission UX issues).

Notes

• macOS-only on this PR. Other platforms keep the existing trait defaults ("not available").
• No protocol-breaking changes to existing computer_use_* tools — the new interactive_* actions live alongside them.