refactor(memory)!: remove the QMD backend; builtin is the only memory engine (#120936)

* refactor(memory): remove qmd backend

Make builtin the sole memory-core engine, rename the retained session helper barrel, retire QMD config with doctor migrations, and remove QMD runtime/UI/policy surfaces.

* docs(memory): remove qmd backend guidance

Delete the QMD concept page, rewrite memory documentation for builtin retrieval, and remove QMD from navigation and taxonomy source.

* refactor(memory): remove qmd-only leftovers

* refactor(memory): finish qmd integration cleanup

* build(deps): align root string-width types

* build(deps): model root string-width tooling

* refactor(memory): align qmd removal ui and docs

* fix(memory): preserve qmd external paths in doctor

* test(memory): remove obsolete backend probe case

* test(plugin-sdk): refresh private type baseline

.github/workflows/codeql-critical-quality.yml

@@ -111,7 +111,6 @@ on:
       - "src/gateway/resolve-configured-secret-input-string*.ts"
       - "src/gateway/security-path*.ts"
       - "src/gateway/server-methods/secrets*.ts"
-      - "src/gateway/server-startup-memory.ts"
       - "src/gateway/method-scopes.ts"
       - "packages/gateway-protocol/src/**"
       - "src/gateway/server-methods/**"
@@ -257,7 +256,7 @@ jobs:
                 packages/gateway-protocol/src/*|packages/gateway-protocol/src/**/*|src/gateway/method-scopes.ts|src/gateway/server-methods/*|src/gateway/server-methods.ts|src/gateway/server-methods-list.ts)
                   gateway=true
                   ;;
-                packages/memory-host-sdk/*|src/commands/doctor/cron/dreaming-payload-migration.ts|src/commands/doctor-memory-search.ts|src/gateway/server-startup-memory.ts|src/memory/*|src/memory-host-sdk/*)
+                packages/memory-host-sdk/*|src/commands/doctor/cron/dreaming-payload-migration.ts|src/commands/doctor-memory-search.ts|src/memory/*|src/memory-host-sdk/*)
                   memory=true
                   ;;
                 src/infra/outbound/base-session-key.ts|src/infra/outbound/delivery-queue*.ts|src/infra/outbound/outbound-session.ts|src/infra/outbound/session-binding*.ts|src/infra/outbound/session-context.ts|src/infra/outbound/targets-session.ts)

.github/workflows/codeql.yml

@@ -28,7 +28,6 @@ on:
       - "extensions/file-transfer/src/**"
       - "extensions/google-meet/src/**"
       - "extensions/imessage/src/**"
-      - "extensions/memory-core/src/memory/qmd-manager.ts"
       - "extensions/memory-wiki/src/obsidian.ts"
       - "extensions/microsoft-foundry/cli.ts"
       - "extensions/ollama/src/wsl2-crash-loop-check.ts"