Add reminders & follow-ups (W1) (v0.1.0:92)

First-class reminders tied to the fundraising grid — foundation of the agreed
reminders -> NL-search -> bot-mutations plan (keep LP data off third-party LLMs).

- reminders table (migration 0006; logical FK to fundraising_investors.id +
  denormalized name), CRUD at /api/reminders (soft-delete; open/done/snoozed/
  cancelled; assignee; source; source_row_id resolution)
- read-only derived reminder_status grid column (overdue/due_soon/open),
  filterable; orphan reconciler cancels reminders when an investor leaves the grid
- Reminders page, Dashboard "Reminders Due" card, daily-digest reminders section
- per-investor last_activity_at recency rollup (shared block for the W2 NL query)
- tests: test_reminders.py + digest reminders test (31/31 green, render-smoke green)

backend/migrations/0006_reminders.sql

@@ -0,0 +1,45 @@
+-- Reminders & follow-ups — a real tickler/task model tied to the fundraising grid.
+--
+-- ADDITIVE + REVERSIBLE (CLAUDE.md guardrail #3): one new table + indexes; nothing
+-- existing is touched. Until now the only follow-up surfaces were the grid's binary
+-- `follow_up` checkbox (no date, owner, or status) and communications.next_action_date
+-- (tied to a single logged comm). This gives investors first-class reminders with a due
+-- date, status lifecycle, assignee, and provenance — the foundation for "who needs a
+-- follow-up?" queries, the daily digest's due/overdue section, and (later) bot-proposed
+-- reminders behind the Matrix approval gate.
+--
+-- investor_id is a LOGICAL foreign key to fundraising_investors(id) — deliberately NOT a
+-- declared SQLite FOREIGN KEY, matching opportunities.fundraising_investor_id (migration
+-- 0005). fundraising_investors rows are upserted by source_row_id on every grid save with
+-- a STABLE id (so the link survives saves), but a row dropped from the grid is DELETEd —
+-- there is nothing to cascade, and reconcile_grid_reminders() cancels the orphans on the
+-- next save (the pipeline reconciler's twin). investor_name is denormalized so a reminder
+-- stays readable in history even after its grid row is gone. investor_id is nullable: a
+-- reminder can be a standalone team task not tied to any investor.
+--
+-- contact_id is an optional logical FK to contacts(id) (the specific person). assignee_id
+-- is a logical ref to users(id) (NULL = team-wide). created_by holds a users.id OR a
+-- non-user sentinel ('bot'/'automation'), so it is plain TEXT with no FK.
+CREATE TABLE IF NOT EXISTS reminders (
+    id            TEXT PRIMARY KEY,
+    investor_id   TEXT,                                   -- logical FK -> fundraising_investors.id (NULL = standalone task)
+    investor_name TEXT,                                   -- denormalized; survives grid-row deletion
+    contact_id    TEXT,                                   -- optional logical FK -> contacts.id
+    title         TEXT NOT NULL,
+    details       TEXT,
+    due_date      TEXT,                                   -- ISO date 'YYYY-MM-DD' (or datetime)
+    status        TEXT NOT NULL DEFAULT 'open',           -- open | done | snoozed | cancelled
+    snoozed_until TEXT,
+    assignee_id   TEXT,                                   -- logical ref -> users.id; NULL = team-wide
+    created_by    TEXT,                                   -- users.id, or 'bot' / 'automation'
+    source        TEXT NOT NULL DEFAULT 'human',          -- human | bot | automation
+    completed_at  TEXT,
+    created_at    TEXT DEFAULT (datetime('now')),
+    updated_at    TEXT DEFAULT (datetime('now')),
+    deleted_at    TEXT
+);
+
+CREATE INDEX IF NOT EXISTS idx_reminders_investor ON reminders(investor_id) WHERE deleted_at IS NULL;
+CREATE INDEX IF NOT EXISTS idx_reminders_status   ON reminders(status)      WHERE deleted_at IS NULL;
+CREATE INDEX IF NOT EXISTS idx_reminders_due      ON reminders(due_date)    WHERE deleted_at IS NULL;
+CREATE INDEX IF NOT EXISTS idx_reminders_assignee ON reminders(assignee_id) WHERE deleted_at IS NULL;