docs: align README with upstream refinements

Update tagline to "One brain. Local or cloud." variant, add SQLite source-of-
truth clarification in Git Sync section, correct MCP tools count from 15 to
19 (table already listed 19 tools). Skipped nav link additions that reference
docs not yet present in this fork (engram-cloud/README.md, CODEBASE-GUIDE.md).

Author: rubenqc

README.md

@@ -4,7 +4,7 @@
 
 <p align="center">
   <strong>Persistent memory for AI coding agents</strong><br>
-  <em>Agent-agnostic. Single binary. Zero dependencies.</em>
+  <em>One brain. Local or cloud. Agent-agnostic, single binary, zero dependencies.</em>
 </p>
 
 <p align="center">
@@ -81,7 +81,7 @@ It gives Pi persistent project memory, compaction recovery, and shared memory wi
 
 Full details on session lifecycle, topic keys, and memory hygiene → [docs/ARCHITECTURE.md](docs/ARCHITECTURE.md)
 
-## MCP Tools (15)
+## MCP Tools (19)
 
 | Category               | Tools                                                                                                            |
 | ---------------------- | ---------------------------------------------------------------------------------------------------------------- |
@@ -91,7 +91,7 @@ Full details on session lifecycle, topic keys, and memory hygiene → [docs/ARCH
 | **Conflict Surfacing** | `mem_judge`, `mem_compare`                                                                                       |
 | **Utilities**          | `mem_save_prompt`, `mem_stats`, `mem_capture_passive`, `mem_merge_projects`, `mem_current_project`, `mem_doctor` |
 
-Full tool reference with parameters → [DOCS.md#mcp-tools-15-tools](DOCS.md#mcp-tools-15-tools)
+Full tool reference with parameters → [DOCS.md#mcp-tools-19-tools](DOCS.md#mcp-tools-19-tools)
 
 ## Terminal UI
 
@@ -112,6 +112,8 @@ engram tui
 
 Share memories across machines. Uses compressed chunks — no merge conflicts, no huge files.
 
+Local SQLite remains the source of truth. Cloud integration is opt-in replication.
+
 ```bash
 engram sync                    # Export new memories as compressed chunk
 git add .engram/ && git commit -m "sync engram memories"