feat(cli): polish TUI interaction, status chrome, and completion

[im10furry]

Summary

Interaction review on beta → feat/interaction-review-opt. Bounded fixes on shipped TUI paths (prompt, overlays, permissions, completion) — no rewrite.

Status, color, display

• Status / hint / overlay copy: /config, /help, model, init, stash, cancel, queue
• Request status: Preparing / Generating; Esc cancel gates
• Permission deny labeled Deny (Esc)
• Tasks detail: Esc goes back instead of closing the overlay
• Chrome contrast: RunningTasks, Help, Logo, ModeIndicator, History, Command Palette, LSP status

Coding path

• Unknown slash commands stay local (no user turn); // is a literal slash
• Config 1–4 prefills only; Help a opens the full catalog
• First Tab on / with multiple matches shows the list
• Delete is forward-delete (not Backspace)

Completion

• Command Enter still insert+submit; file / @ Enter insert only (dirs follow up like →)
• Tab cycle keeps the original typed word so Esc can restore it
• @ only at a token boundary (user@host is not a mention)
• @src/ and @~/… are file mentions (do not load all agents)
• @src without a slash ranks a cwd src/ file above unrelated agents; prefix-matching agents still win
• A directory name without a trailing slash is a candidate (docs/), not an implicit listing
• ~ uses os.homedir(); \ is a path separator
• Empty-dir hint actually shows on the status line: No files in docs/
• Help copy matches keys: Tab accept / Enter send for commands; insert path / mention; open folder

Test plan

• Completion unit: context, fileSuggestions, generateSuggestions, copy, tab/auto-trigger/hook
• tui-interactions.completionNavigation e2e (Tab cycle + Esc restore, Enter file insert, empty-dir timer)
• PromptInputView / CompletionPanel help + empty-dir status line
• slashCommand / processUserInput unknown-command / disable-slash-commands
• CI on this PR

[im10furry]

已合并入 beta（f95e1591），后续统一由 #239（beta → main）进入主线。