Add in-progress state to tasks

Introduce IN_PROGRESS as a new task state between TODO and DONE across
the full stack: database enum, Go backend, GraphQL, MCP, and frontend.

The task state icon now cycles forward on click (TODO → IN_PROGRESS →
DONE → TODO), and the action dropdown provides explicit "Move to"
options for any state transition. The "All" tab supports drag-and-drop
between state sections to change a task's state.

Signed-off-by: Sacha Al Himdani <sacha@getprobo.com>

pkg/coredata/migrations/20260402T120000Z.sql

@@ -0,0 +1,15 @@
+-- Copyright (c) 2025-2026 Probo Inc <hello@getprobo.com>.
+--
+-- Permission to use, copy, modify, and/or distribute this software for any
+-- purpose with or without fee is hereby granted, provided that the above
+-- copyright notice and this permission notice appear in all copies.
+--
+-- THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+-- REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+-- AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+-- INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+-- LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+-- OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+-- PERFORMANCE OF THIS SOFTWARE.
+
+ALTER TYPE task_state ADD VALUE 'IN_PROGRESS' BEFORE 'DONE';