Converge the chat onto the SDK's shared derivations and ChatTurn grouping

[hbrooks]

Finishes DRYing session rendering between the CLI and the web app onto @ellipsis-dev/sdk 0.16.0 (ellipsis#6389).

• Repoints the SDK from the file: link to ^0.16.0 (now on npm) and seeds stores via seedTranscriptStore instead of hand-built snapshot/records_append frames.
• Deletes ConnectApp's copies of deriveSandboxState, sessionLogText, awaitingAgentPhase, deliveredUnechoedSends, sandboxSummary, lastLines, hookPhrase, humanDuration and the SandboxState types; imports them from @ellipsis-dev/sdk/store. sessionLogText and deriveSandboxState are wrapped in src/lib/steps.ts to swap the store's middot separators for commas, so the terminal copy is unchanged (same pattern lifecycleText already used).
• Replaces reshapeTranscript with the SDK's ChatTurn grouping: the chat now consumes groupRecordsToChatTurns (store.chatTurns(), the same objects the web's SessionChat renders, mapped to transcript items in src/lib/chatItems.ts. Turn errors render from turn.isError; the wake line still settles in place under the same key; the undisplayed-records counter is preserved (undisplayedRecordCount). --no-records groups a filtered record slice since turns carry no feed_seq.
• The verbose steps path (session records / renderFrameHuman) stays on recordToItems/formatStepLine, untouched.
• Tests: the moved derivations are tested in the SDK now; the CLI keeps comma-wording tests through the wrappers plus new chatTurnsToItems/undisplayedRecordCount coverage.

Casts worth a look: seedTranscriptStore call sites cast the REST page to the frame types (REST marks nullable fields optional, frames require them; same JSON either way). If that grates, an SDK follow-up could accept the REST flavor directly.
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