fix: terminal content duplication on WebSocket reconnect (v0.35.50)

[jpelaez-23blocks]

Summary

• Terminal reconnect fix: Clear terminal buffer on WebSocket reconnect before fresh history arrives. Prevents content duplication that made high-output agents (jarvis) unusable — history was appended on top of existing content every 30-40s.
• Chat paste-probe delivery: sendChatMessage() uses tmux buffer paste with poll-based verification instead of send-keys -l. Blocks sending at permission prompts.
• Chat sending vs thinking state: "Sending..." (blue) and "Thinking..." (amber) are now distinct activity states in both desktop and mobile chat views.
• Tab validation: localStorage active tab validated against known tabs on load, preventing blank content from stale values.

Root Cause (Terminal)

When a WebSocket disconnects (heartbeat timeout, network blip), the server sends 5000 lines of tmux capture-pane history on reconnect. The client never cleared the terminal buffer first — history was appended to existing content. For jarvis (Claude Opus thinking animation producing dense ANSI output), this caused a full visual re-render every ~35 seconds.

Test plan

• Open jarvis terminal — should no longer duplicate content on reconnect
• Disconnect network briefly, reconnect — terminal shows clean history without duplication
• Chat: send message while agent is at permission prompt — should show error
• Chat: send message — should show "Sending..." then "Thinking..."
• Remove aimaestro-active-tab from localStorage, set to invalid value, reload — should default to chat

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