feat: Folder name in tabs + editable session name (#8)

[pitimon]

Summary

• Restructure session tabs to two-row layout: top row has status/name/actions, bottom row shows working directory folder name
• Folder name displays with 📁 icon and tooltip showing full path
• Folder row hidden on mobile for compact display
• Add "Session Name" input field in the Context tab of Session Options modal
• Auto-saves on blur using the existing PUT /api/sessions/:id/name endpoint
• Right-click inline rename still works as before

Fixes #8

Changes

styles.css:

• .session-tab: changed to flex-direction: column layout
• New classes: .tab-row-header, .tab-actions-inline, .tab-folder, .tab-folder-icon
• Mobile: .tab-folder { display: none } + revert to row layout

app.js:

• _fullRenderSessionTabs(): restructured tab HTML with tab-row-header wrapper and tab-folder span
• openSessionOptions(): populates modalSessionName input with current name
• New saveSessionNameFromModal(): saves name via PUT API on input blur

index.html:

• Added Session Name input field before Appearance section in Context tab

Test plan

• Build passes (npm run build)
• Session tabs show folder name below session name
• Folder tooltip shows full working directory path
• Session Name input appears in Context tab of Session Options
• Editing session name and blurring saves automatically
• Clearing session name reverts tab to folder name display
• Right-click inline rename still works on tabs
• Mobile: folder row is hidden, tabs remain compact
• No visual regressions with subagent badges and task badges

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