feat(tui): Agent Hub TUI — browse, search, launch, and manage agents

[kovtcharov-amd]

Running gaia.exe with no args now opens the Agent Hub — a terminal-native hub for discovering, searching, and launching GAIA agents. Before: the Go TUI only supported gaia chat --subprocess <binary>. After: users get a full agent browser with dashboard, fuzzy search, voting, and agent lifecycle management, all in a ~21MB standalone binary with <200ms startup.

Depends on: #985 (gaia-bash --json-events mode)

Test plan

• cd tui && go test ./... -v — 45 tests pass (catalog, client, event, smoke)
• go vet ./... — clean
• .\bin\gaia.exe — hub opens, browse Bash agent, Tab to Available/Coming Soon
• .\bin\gaia.exe chat --subprocess "path\to\gaia-bash.exe --json-events --model Gemma-4-E4B-it-GGUF" — real LLM chat works
• Hub: / search, d delete with confirm, v vote, ? help, q quit
• Chat: multi-turn, /help /hub /clear, perf stats (duration/TTFT/tok/s), Esc to cancel

[kovtcharov-amd]

Ready for review — Agent Hub TUI

Two PRs ready together:

1. feat(cpp): gaia-bash — native C++ bash coding agent with TUI, API server, MCP server #985 — gaia-bash native agent: adds --json-events mode to the C++ bash agent so TUI/WebUI can consume structured JSONL events instead of raw terminal output.

2. feat(tui): Agent Hub TUI — browse, search, launch, and manage agents #1186 — Agent Hub TUI: Go terminal UI that serves as the central hub for browsing, searching, and launching GAIA agents. Standalone ~21MB binary, <200ms startup.

What it does: Run gaia.exe → see the Agent Hub with a dashboard, fuzzy search, agent categories (Installed/Available/Coming Soon), voting on upcoming agents. Select an agent → launches into a chat TUI with live streaming, Rich-style answer panels, perf stats (TTFT, tok/s). Esc returns to the hub.

How to test:

cd tui
go build -o bin/gaia.exe ./cmd/gaia
go build -o bin/mockagent.exe ./test/mockagent

# Hub with mock agent (no LLM needed):
./bin/gaia.exe --mock "./bin/mockagent.exe"

# Hub with real LLM (needs Lemonade + gaia-bash from #985):
./bin/gaia.exe

# Direct chat with real LLM:
./bin/gaia.exe chat --subprocess "path/to/gaia-bash --json-events --model Gemma-4-E4B-it-GGUF"

Merge #985 first, then #1186.

[itomek]

Reviewed at a structural/triage level (no Go toolchain here to build). Cleanly isolated: all 33 substantive files live under tui/, with a CI workflow and a Go smoke test (tui/test/smoke_test.go) included; nothing touches the Python package. As the description notes, this depends on #985, so it should land after it. Approving on structure and scope; a go build + go test gate in CI would be worth adding so the TUI doesn't rot untested.

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Generated by Claude Code

[kovtcharov-amd]

@claude review this PR.