Add durable startup memory context

[coe0718]

Summary

Adds a small startup-only durable memory section for brand-new sessions so Phantom begins with a bit of long-term continuity before normal retrieval takes over.

What Changed

• passes isNewSession from the runtime into the memory context builder on the first turn of a fresh session
• adds a compact Durable Context section that only appears on new sessions
• selects durable facts from the normal semantic recall using high confidence filtering
• adds a metadata-ranked episodic recall pass for startup memories and deduplicates those memories from the normal sections
• preserves stale low-signal episodic filtering from the current main branch during normal context injection
• documents the new startup behavior in docs/memory.md

Why

This keeps the contribution focused on startup retrieval rather than adding a parallel memory system. It gives new sessions more continuity while staying aligned with the existing episodic + semantic + procedural memory design.

Testing

• bash -lc 'export PATH="$HOME/.bun/bin:$PATH" && /home/coemedia/.bun/bin/bun test src/memory/__tests__/context-builder.test.ts'
• bash -lc 'export PATH="$HOME/.bun/bin:$PATH" && /home/coemedia/.bun/bin/bun test'
• /home/coemedia/.bun/bin/bun run typecheck
• /home/coemedia/.bun/bin/bun run lint

Notes

• Rebasing onto current main required carrying forward the startup-only durable context while preserving the newer stale-memory filtering already merged in context-builder.ts.

[mcheemaa]

#2 just landed on main. Can you rebase this on main when you get a chance? Will review once it's updated.

[coe0718]

Rebased