phase B (1/4): CSV parser + InstrumentMap (T212 shortcode → Yahoo ticker)

First two slices of the multi-user roadmap (Phase B). Validates the
core onboarding mechanic against the user's real T212 export before
paying any auth/tenancy tax.

CSV parser (app/services/csv_import.py):
  - Header-name matched (survives T212 reordering columns between
    exports), tolerant of UTF-8 BOM, dash/N/A/empty markers, thousand-
    separator commas, blank rows, zero-quantity stubs, missing Total row.
  - Returns ParsedPie(name, positions, invested, value, result) with
    derived avg_price + current_price per share in account currency.
  - 14 tests covering happy path on the real CSV + 13 edge cases.

InstrumentMap (migration 0006 + app/services/instrument_map.py):
  - Catalogue table mapping T212 ticker → Yahoo ticker, populated by
    sync_from_t212() against the dev's read-only API key. Manual rows
    (manual=True) are protected from auto-overwrite.
  - Pure t212_ticker_to_yahoo() handles both suffix forms: single
    trailing exchange letter (l/a/p/d/m/s/...) and country code (US,
    DE, FR, IT, CA, ...). All 13 of the user's holdings + 15 case-
    coverage tests pass.
  - Live sync against T212 ingests 17,050 instruments (~2.2% unmappable
    on exotic exchanges; can extend the suffix map later).
  - resolve_slice() picks the right listing per shortName using a
    UK-friendly currency preference (GBX > GBP > EUR > USD). Resolved
    correctly for all 13 of the user's positions, including TTE on
    Paris vs the NYSE dual-listing.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

alembic/versions/0006_instrument_map.py

@@ -0,0 +1,49 @@
+"""instrument_map — T212 shortcode → Yahoo ticker mapping
+
+Revision ID: 0006
+Revises: 0005
+Create Date: 2026-05-16
+"""
+from typing import Sequence, Union
+
+import sqlalchemy as sa
+from alembic import op
+
+
+revision: str = "0006"
+down_revision: Union[str, None] = "0005"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.create_table(
+        "instrument_map",
+        sa.Column("id", sa.BigInteger, primary_key=True, autoincrement=True),
+        # T212's internal ticker (e.g. "SGLNl_EQ", "EQNR_US_EQ"). Unique
+        # globally because each T212 ticker is one listing.
+        sa.Column("t212_ticker", sa.String(64), nullable=False),
+        # T212's short name (e.g. "SGLN") — the value in the CSV's "Slice"
+        # column. Not unique: many tickers share a shortName across listings.
+        sa.Column("t212_shortname", sa.String(32), nullable=False),
+        # Computed Yahoo Finance symbol. Nullable so unmappable rows still
+        # land in the table (we may add manual mappings later).
+        sa.Column("yahoo_ticker", sa.String(32)),
+        sa.Column("name", sa.String(128), nullable=False),
+        # T212's currencyCode (GBP, GBX, USD, EUR, CHF, …).
+        sa.Column("currency", sa.String(8)),
+        sa.Column("isin", sa.String(16)),
+        sa.Column("instrument_type", sa.String(16)),       # STOCK, ETF, …
+        # True when the row was hand-edited; auto-sync won't overwrite.
+        sa.Column("manual", sa.Boolean, nullable=False, server_default=sa.text("0")),
+        sa.Column("last_verified_at", sa.DateTime(timezone=True), nullable=False),
+        sa.UniqueConstraint("t212_ticker", name="uq_imap_t212_ticker"),
+    )
+    op.create_index("ix_imap_shortname", "instrument_map", ["t212_shortname"])
+    op.create_index("ix_imap_isin", "instrument_map", ["isin"])
+
+
+def downgrade() -> None:
+    op.drop_index("ix_imap_isin", table_name="instrument_map")
+    op.drop_index("ix_imap_shortname", table_name="instrument_map")
+    op.drop_table("instrument_map")