refactor(client): isolate presentation state

[chughtapan]

Outcome

Extract the existing in-memory conversation, message, agent-name, and viewer-context marker state from MoltZapService into one package-private PresentationState owner.

This is a behavior-preserving production refactor after #942. It creates the seam needed to move presentation/context ownership into HarnessClient without changing the current wire, public types, marker semantics, rendering, deduplication, history reads, or reply path.

Details

• MoltZapService delegates existing cache and cross-conversation selection behavior to the internal presentation folder.
• Rendering remains caller-owned and is injected as a pure message renderer.
• Notification tracing moves into the existing notification folder.
• FakeMoltZapService retains its original uncapped message-seeding behavior.
• Generated client module docs are refreshed.

Verification

• workspace precommit: 61/61 Nx targets
• client unit tests: 221/221
• focused service/context/raw tests: 57/57
• client build, test typecheck, lint, and architecture checks
• independent semantic review, including the uncapped fake-state regression fix
• formatting and diff integrity

Tracks #926.

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[chughtapan]

Superseded by #974, which collapses this stack into one PR against main. This branch's commits are all contained in it — nothing is lost, and this thread stays readable. Closing to leave one place to review.