Improve session copy, filtering, and dialog behavior

[milanshen]

Context

CoSlash’s session UI mixes internal terminology with ambiguous cost, state, and handoff labels. This update makes the language more direct, aligns summaries and board layouts with active filters, and removes redundant or distracting UI behavior.

Changes

Copy and messaging

• Clarify session, subagent, timeline, handoff, cost, and readiness terminology.
• Improve loading, failure, search, and empty-state messages.

Filtering and board layout

• Make summary costs and session counts follow the vendor filter.
• Hide empty board status columns and expand the remaining columns.

UI cleanup

• Remove the redundant page footer.
• Prevent the session UUID tooltip from appearing automatically when the inspector opens.
• Move the subagent context note below the dialog title and remove its redundant footer and Close button.

Test

• Verified summary costs and counts across All vendors, Claude Code, and Codex.
• Verified vendor-filtered board views hide empty status columns and reflow correctly.
• Verified the session inspector opens without showing the UUID tooltip.
• Verified the subagent dialog note placement and removal of the footer.

Screenshots

• Sessions list and inspector — updated copy and removed footer

• Board view — filtered totals and empty status columns hidden

- Subagent dialog — context note below title with no footer