docs: separate public manual from internal project documentation

docs/product-overview.md

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+# What ThothII does
+
+ThothII helps turn a natural-language question into reviewed SQL. It is intended for
+people who know the meaning of their data and need to make the assumptions behind a
+query explicit. The model proposes; a human reviewer approves, corrects or rejects.
+
+## From a question to a reusable result
+
+The [eight-phase workflow](skills.md) clarifies the question, consults reusable knowledge,
+selects relevant Evidence and database objects, prepares a query plan, and produces SQL
+for review. Approved knowledge can be saved for later questions.
+
+- **Workspace:** the domain context and its Evidence configuration.
+- **Database catalog:** tables, columns, relationships and reviewed descriptions.
+- **Evidence:** domain sources and rules with provenance that a reviewer can inspect.
+- **Memory:** reusable clarifications, SQL rules, solved questions and explained errors.
+- **Session:** the saved artifacts and decisions for one question, not a permanent chat transcript.
+
+Resuming a session uses its saved state. Model output is a proposal, not a guarantee of
+correctness: review the scope, assumptions, sources and SQL before relying on the result.
+
+## What an installation includes
+
+The Docker stack includes the web application, its runtime, a PostgreSQL metadata/Memory
+catalog, Qdrant and the embedding service. A browser is the normal user interface; the
+host `tht` command is used to configure and operate the installation.
+
+The data warehouse and generative model endpoints are configured separately. Docker
+does not supply their credentials, network access or domain data. A standalone installation
+is therefore self-hosted, but is not automatically offline or independent of those services.
+Review data-access permissions and the model-provider configuration before using real data.
+
+## Choose your next step
+
+- Install on Mac, Windows through WSL2, or Linux: [Italian](install/standalone-manual-it.md)
+  or [English](install/standalone-manual-en.md) manual procedure.
+- Configure [display mode and language](install/shell-and-language.md),
+  [authentication](install/authentication-local.md) and [models](general/pi-configuration.md).
+- Prepare [workspaces](operations/workspaces.md) and [databases](operations/database-management.md).
+- Start a reviewed question using the [user guide](guida-utente.md).
+
+The installation guides state the platform tests still to complete. Availability of a
+procedure is not a certification that every target machine has been tested.