Persona-first TUI: name and identity as the primary TUI anchor

[hai-pilgrim]

Context

The current TUI is model-first and tool-first. The persona/character name appears only in the pet avatar area (if a custom pet is configured). For clanker-code, the identity of who you are talking to should be the primary visual anchor — not a footnote buried in pet configuration.

Related: #33 covers the character picker and status surface. This issue is specifically about making the active session TUI layout persona-first, not just the selection flow.

What is needed

1. Prominent persona name display. The active character name (e.g. "Pilgrim", "HAI", "C3PH0") should be visible at all times in the TUI — in the header, status bar, or a dedicated identity panel. Not just as a pet label.

2. Identity-aware greeting and context. When a session starts, the TUI should reflect who the persona is — name, possibly a one-line bio from the character manifest, and the persona's avatar. This replaces the generic "How can I help you?" with something persona-appropriate.

3. Visual distinction between personas. If a user switches personas (via picker Character picker, status surface, and anonymous session adoption #33 or AGENT_PERSONA Read AGENT_PERSONA envvar as first-class identity input and select histories by persona name #40), the TUI should visually reflect the change — different color accent, avatar, and name.

Relationship to existing issues

• Character picker, status surface, and anonymous session adoption #33 (character picker/status) — covers selection UI. This covers session-time identity display.
• Read AGENT_PERSONA envvar as first-class identity input and select histories by persona name #40 (AGENT_PERSONA envvar) — covers the input mechanism. This covers TUI rendering of that identity.
• Room is a manifest field with no runtime: half-block room composition unimplemented #37 (room composition) — rooms could eventually frame the persona-first layout.

Acceptance criteria

• Active persona name is always visible in the TUI (header or status bar)
• Persona identity is shown on session start (name + avatar + optional bio)
• Switching persona visually updates the TUI identity elements
• Works with both --name/AGENT_PERSONA and interactive picker flows