refactor(transform): remove raw layer, read landing zone directly

- Delete 6 data raw models (coffee_prices, cot_disaggregated, ice_*,
  psd_data) — pure read_csv passthroughs with no added value
- Move 3 PSD seed models raw/ → seeds/, rename schema raw.* → seeds.*
- Update staging.psdalldata__commodity: read_csv(@psd_glob()) directly,
  join seeds.psd_* instead of raw.psd_*
- Update 5 foundation models: inline read_csv() with src CTE, removing
  raw.* dependency (fct_coffee_prices, fct_cot_positioning, fct_ice_*)
- Remove fixture-based SQLMesh test that depended on raw.cot_disaggregated
  (unit tests incompatible with inline read_csv; integration run covers this)
- Update readme.md: 3-layer architecture (staging/foundation → serving)

Landing files are immutable and content-addressed — the landing directory
is the audit trail. A raw SQL layer duplicated file bytes into DuckDB
with no added value.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

transform/sqlmesh_materia/models/foundation/fct_coffee_prices.sql

@@ -1,6 +1,7 @@
 -- Foundation fact: daily KC=F Coffee C futures prices.
 --
--- Casts raw varchar columns to proper types and deduplicates via hash key.
+-- Reads directly from the landing zone, casts varchar columns to proper types,
+-- and deduplicates via hash key.
 -- Covers all available history from the landing directory.
 --
 -- Grain: one row per trade_date.
@@ -17,7 +18,18 @@ MODEL (
   cron '@daily'
 );
 
-WITH cast_and_clean AS (
+WITH src AS (
+  SELECT * FROM read_csv(
+    @prices_glob(),
+    compression   = 'gzip',
+    header        = true,
+    union_by_name = true,
+    filename      = true,
+    all_varchar   = true
+  )
+),
+
+cast_and_clean AS (
   SELECT
     TRY_CAST(Date AS date)        AS trade_date,
     TRY_CAST(Open AS double)      AS open,
@@ -32,7 +44,7 @@ WITH cast_and_clean AS (
 
     -- Dedup key: trade date + close price
     hash(Date, Close)              AS hkey
-  FROM raw.coffee_prices
+  FROM src
   WHERE TRY_CAST(Date AS date) IS NOT NULL
     AND TRY_CAST(Close AS double) IS NOT NULL
 ),