bd create: support --description=- for stdin input

Allows descriptions with apostrophes and other shell-problematic
characters by reading from stdin. Works with both --description=-
and --body=- (the GitHub CLI-style alias).

Example: echo "It's working" | bd create --title "Test" --description=-

Also fixes pre-existing duplicate pinned column/variable declarations.

Fixes beads-iwi

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/storage/sqlite/schema.go

@@ -34,8 +34,6 @@ CREATE TABLE IF NOT EXISTS issues (
     pinned INTEGER DEFAULT 0,
     -- NOTE: replies_to, relates_to, duplicate_of, superseded_by removed per Decision 004
     -- These relationships are now stored in the dependencies table
-    -- Workflow fields
-    pinned INTEGER DEFAULT 0,
     CHECK ((status = 'closed') = (closed_at IS NOT NULL))
 );