feat(ready,blocked): Add --parent flag for scoping by epic/bead desce… (#743)

* feat(ready,blocked): Add --parent flag for scoping by epic/bead descendants

Add --parent flag to `bd ready` and `bd blocked` CLI commands and MCP tools
to filter results to all descendants of a specific epic or bead.

## Backward Compatibility

- CLI: New optional --parent flag; existing usage unchanged
- RPC: New `blocked` operation added (was missing); existing operations unchanged
- MCP: New optional `parent` parameter; existing calls work as before
- Storage interface: GetBlockedIssues signature changed to accept WorkFilter
  - All callers updated to pass empty filter for existing behavior
  - Empty WorkFilter{} returns identical results to previous implementation

## Implementation Details

SQLite uses recursive CTE to traverse parent-child hierarchy:

    WITH RECURSIVE descendants AS (
        SELECT issue_id FROM dependencies
        WHERE type = 'parent-child' AND depends_on_id = ?
        UNION ALL
        SELECT d.issue_id FROM dependencies d
        JOIN descendants dt ON d.depends_on_id = dt.issue_id
        WHERE d.type = 'parent-child'
    )
    SELECT issue_id FROM descendants

MemoryStorage implements equivalent recursive traversal with visited-set
cycle protection via collectDescendants helper.

Parent filter composes with existing filters (priority, labels, assignee, etc.)
as an additional WHERE clause - all filters are AND'd together.

## RPC Blocked Support

MCP beads_blocked() existed but daemon client raised NotImplementedError.
Added OpBlocked and handleBlocked to enable daemon RPC path, which was
previously broken. Now both CLI and daemon clients work for blocked queries.

## Changes

- internal/types/types.go: Add ParentID *string to WorkFilter
- internal/storage/sqlite/ready.go: Add recursive CTE for parent filtering
- internal/storage/memory/memory.go: Add getAllDescendants/collectDescendants
- internal/storage/storage.go: Update GetBlockedIssues interface signature
- cmd/bd/ready.go: Add --parent flag to ready and blocked commands
- internal/rpc/protocol.go: Add OpBlocked constant and BlockedArgs type
- internal/rpc/server_issues_epics.go: Add handleBlocked RPC handler
- internal/rpc/client.go: Add Blocked client method
- integrations/beads-mcp/: Add BlockedParams model and parent parameter

## Usage

  bd ready --parent bd-abc              # All ready descendants
  bd ready --parent bd-abc --priority 1 # Combined with other filters
  bd blocked --parent bd-abc            # All blocked descendants

## Testing

Added 4 test cases for parent filtering:
- TestParentIDFilterDescendants: Verifies recursive traversal (grandchildren)
- TestParentIDWithOtherFilters: Verifies composition with priority filter
- TestParentIDWithBlockedDescendants: Verifies blocked issues excluded from ready
- TestParentIDEmptyParent: Verifies empty result for childless parent

* fix: Correct blockedCmd indentation and suppress gosec false positive

- Fix syntax error from incorrect indentation in blockedCmd Run function
- Add nolint:gosec comment for GetBlockedIssues SQL formatting (G201)
  The filterSQL variable contains only parameterized WHERE clauses with
  ? placeholders, not user input

internal/types/types.go

@@ -646,6 +646,9 @@ type WorkFilter struct {
 	LabelsAny  []string   // OR semantics: issue must have AT LEAST ONE of these labels
 	Limit      int
 	SortPolicy SortPolicy
+
+	// Parent filtering: filter to descendants of a bead/epic (recursive)
+	ParentID *string // Show all descendants of this issue
 }
 
 // StaleFilter is used to filter stale issue queries