feat(gui): add v2 capability badges in provider panel

Phase 5 t5_4 (UI adaptations for 11 v2 fields): the simplest
honest adaptation — render small colored badges for the 11
v2 fields where the active vendor+model supports them. Each
badge has a tooltip showing the field name.

The 11 fields:
  reasoning, structured_output, code_execution, web_search,
  x_search, file_search, mcp_support, audio, video,
  grounding, computer_use

A new module-level function _render_v2_capability_badges(caps)
is added to src/gui_2.py (per the HARD RULE on no new
src/<thing>.py files). It's called from render_provider_panel
right after the existing '[Local]' badge (which uses the
runtime override for caps.local).

What this is NOT: a full UI for the 11 fields (per-field
toggles, panels, attachment buttons). Those are design-heavy
work and need their own track. This change gives the user
visibility into which capabilities the active vendor+model
supports, so they can make informed decisions about which
prompts/features to use.

For example, when the user selects qwen-audio, they'll see:
  Provider: qwen [Local]  Capabilities [Audio]
Which makes it obvious they can attach audio files.

Tests:
- 2 new tests in tests/test_vendor_capabilities.py:
  * All 11 v2 fields are present in the helper (drift guard)
  * Helper is a no-op on empty caps (no fields True)
- 118/118 vendor+tool+provider+import-isolation tests pass
  (no regressions; +2 new tests this commit)
- 3 audit scripts pass

tests/test_vendor_capabilities.py

@@ -193,3 +193,30 @@ def test_deepseek_wildcard_falls_back_to_v3_defaults() -> None:
  caps = get_capabilities('deepseek', 'deepseek-future-unregistered')
  assert caps.reasoning is True
  assert caps.structured_output is True
+
+def test_v2_capability_badge_helper_contains_all_11_v2_fields() -> None:
+ """The GUI's v2 capability badges should render badges for all
+ 11 v2 fields. This test ensures the helper stays in sync with
+ the v2 matrix."""
+ import src.gui_2
+ import inspect
+ src_lines: str = inspect.getsource(src.gui_2._render_v2_capability_badges)
+ known_v2_fields: list[str] = [
+  "reasoning", "structured_output", "code_execution",
+  "web_search", "x_search", "file_search", "mcp_support",
+  "audio", "video", "grounding", "computer_use",
+ ]
+ for field in known_v2_fields:
+  assert f'"{field}"' in src_lines, f'v2 field {field!r} missing from _render_v2_capability_badges helper'
+
+def test_v2_capability_badge_helper_skips_disabled_fields() -> None:
+ """Sanity: a caps with all v2 fields False should produce no
+ badges. We can verify this by passing a default-constructed
+ VendorCapabilities and asserting the helper returns without
+ erroring. (We can't easily verify the ImGui output without
+ a live context, but we can verify the helper is a no-op on
+ the no-cap case.)"""
+ from src.gui_2 import _render_v2_capability_badges
+ from src.vendor_capabilities import VendorCapabilities
+ empty_caps = VendorCapabilities(vendor='test', model='empty')
+ _render_v2_capability_badges(empty_caps)