docs: add talk-to-data case study

Add anonymized architecture, governance examples, diagrams, and interview materials.\n\nCo-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

marts_quotes.sql

@@ -0,0 +1,113 @@
+{{
+    config(
+        materialized='table',
+        database=target.database,
+        schema='transform',
+        tags=['semantic_layer', 'chatbot']
+    )
+}}
+
+with source_quotes as (
+    select
+        [REDACTED: quote_id column],
+        [REDACTED: line_item column],
+        [REDACTED: customer_id column],
+        [REDACTED: material_id column],
+        [REDACTED: quantity column],
+        [REDACTED: net_value column],
+        [REDACTED: quote_date column],
+        [REDACTED: sales_person_id column],
+        [REDACTED: source_timestamp column]
+    from [REDACTED: SOURCE_SCHEMA].[REDACTED: QUOTE_TABLE]
+    where [REDACTED: date_partition] >= dateadd(day, -1, current_date())
+),
+
+enrich_product_portfolio as (
+    select
+        sq.quote_id,
+        sq.line_item,
+        sq.customer_id,
+        sq.material_id,
+        sq.quantity,
+        sq.net_value,
+        sq.quote_date,
+        sq.sales_person_id,
+        /* Product portfolio classification */
+        case
+            when sq.material_id like '[REDACTED: pattern 1]%' then 'data-integration'
+            when sq.material_id like '[REDACTED: pattern 2]%' then 'automation'
+            when sq.material_id like '[REDACTED: pattern 3]%' then 'connectivity'
+            else 'other'
+        end as portfolio_code,
+        pm.portfolio_name,
+        pm.portfolio_category,
+        pm.material_description
+    from source_quotes sq
+    left join {{ ref('dim_product_master') }} pm
+        on sq.material_id = pm.material_id
+),
+
+calculate_discounts as (
+    select
+        epf.*,
+        /* Discount hierarchy: customer segment -> discount tier */
+        coalesce(cd.discount_tier_pct, 0) as discount_hierarchy_pct,
+        /* Customer-specific negotiated discount */
+        coalesce(cd.customer_discount_pct, 0) as discount_customer_pct,
+        /* Agreement-based discounts (volume, multi-year, etc.) */
+        coalesce(ca.agreement_discount_pct, 0) as discount_agreement_pct,
+        /* Maximum allowed discount (governance constraint) */
+        cd.discount_ceiling_pct,
+        /* Total discount calculation */
+        coalesce(cd.discount_tier_pct, 0) +
+        coalesce(cd.customer_discount_pct, 0) +
+        coalesce(ca.agreement_discount_pct, 0) as discount_total_pct
+    from enrich_product_portfolio epf
+    left join {{ ref('dim_customer_discount_policy') }} cd
+        on epf.customer_id = cd.customer_id
+        and epf.portfolio_code = cd.portfolio_code
+    left join {{ ref('fct_agreement_discounts') }} ca
+        on epf.customer_id = ca.customer_id
+        and epf.material_id = ca.material_id
+),
+
+governance_flags as (
+    select
+        cd.*,
+        /* Flag: discount exceeds policy maximum */
+        case
+            when cd.discount_total_pct > cd.discount_ceiling_pct
+            then cd.discount_total_pct - cd.discount_ceiling_pct
+            else 0
+        end as discount_above_ceiling,
+        /* Governance indicator: quote ready for human review */
+        case
+            when cd.discount_total_pct > cd.discount_ceiling_pct then 1
+            else 0
+        end as requires_exception_approval
+    from calculate_discounts cd
+)
+
+select
+    quote_id,
+    line_item,
+    customer_id,
+    material_id,
+    portfolio_code,
+    portfolio_name,
+    material_description,
+    quantity,
+    net_value,
+    discount_hierarchy_pct,
+    discount_customer_pct,
+    discount_agreement_pct,
+    discount_total_pct,
+    discount_ceiling_pct,
+    discount_above_ceiling,
+    requires_exception_approval,
+    quote_date,
+    sales_person_id,
+    current_timestamp() as dbt_loaded_at
+from governance_flags
+
+-- ponytail: materialized as table for chatbot + BI queries (not incremental yet; append-only refresh if needed later)