feat: conversation-aware thinking phrases in ThinkingIndicator

[diberry]

Summary

Adds conversation-aware thinking phrases to the CLI's ThinkingIndicator. When a session has prior conversation history, the rotating phrases shift from generic ("Routing to agent", "Analyzing your request") to context-aware phrases ("Reviewing conversation context", "Connecting to previous work"), giving users immediate feedback that the system recognizes ongoing conversation.

Closes #360

Motivation

During multi-turn sessions, the [pending] / thinking indicator shows the same generic phrases regardless of conversation state. Users can't tell whether the system treats their message as part of an ongoing thread or a fresh request. Context-aware phrases solve this at the earliest visible moment — before the coordinator even responds.

What Changed

File	Change
ThinkingIndicator.tsx	Added CONVERSATION_PHRASES array (15 phrases) and hasConversation prop. When true, cycles conversation-aware phrases instead of generic ones.
MessageStream.tsx	Added hasConversation to props interface and passes it through to ThinkingIndicator.
App.tsx	Derives hasConversation from messages array (true when at least one agent response exists). Passes to MessageStream.

3 files changed, 38 insertions, 4 deletions.

UX Before / After

First message of session (no change)

⠋ Routing to agent... (2s)
⠹ Analyzing your request... (5s)
⠼ Reviewing project context... (8s)

Second+ message — Before

⠋ Routing to agent... (2s)
⠹ Analyzing your request... (5s)
⠼ Reviewing project context... (8s)

Second+ message — After

⠋ Reviewing conversation context... (2s)
⠹ Connecting to previous work... (5s)
⠼ Analyzing how this relates... (8s)

Documentation Impact

• No documentation changes needed
• Behavior is self-documenting (users see the phrases in the CLI)

Testing

• Build: npm run build passes (0 errors)
• Tests: 3,944 tests passing across 150 files; 2 pre-existing failures unrelated to this change (Docker-dependent aspire test, missing astro CLI for docs build)
• Manual verification: Start a Squad session, send a message, observe generic phrases. Send a second message, observe conversation-aware phrases.
• Existing ThinkingIndicator tests continue to pass (they don't set hasConversation, so they exercise the default false path)

Rollback Plan

Revert the single commit — removes CONVERSATION_PHRASES, hasConversation prop, and the derivation in App.tsx.

Independence

This PR is fully independent of PR #361 (coordinator prompt change). They address different layers:

• PR feat: add task context classification to coordinator acknowledgment #361 changes what the coordinator says (after thinking completes)
• This PR changes what the user sees (during the thinking/pending phase)

Either can be merged independently with full value.

Review Checklist

• Conversation-aware phrases feel natural and informative
• hasConversation derivation is correct (checks for role === 'agent' in messages)
• Default behavior unchanged for first message (no regression)
• Props are properly threaded through App → MessageStream → ThinkingIndicator

[diberry]

@bradygaster I like the impact of this one but not sure about the implementation of the const strings.