Bump to 0.4.0: worksheet & dashboard intelligence

[PrigasG]

Phase 1 — Bug fixes & consolidation:

• Centralise clean_table/clean_field into .twb_clean_table()/.twb_clean_field() in utils.R; remove 4 duplicate copies across fields.R, calculated_fields.R, relationships.R, joins.R, dependency_graph.R
• Fix plot_relationship_graph() edge direction (from used right_field, not left_field)
• Fix plot_source_join_graph() column references (left_source → left_table)
• Fix integer_ typo in insights.R zone dimension parsing
• Add relationship = 'many-to-many' to inner_join calls in infer_implicit_relationships()

Phase 2 — Per-worksheet intelligence (R/sheet_details.R):

• twb_sheet_shelves(): rows, cols, and encoding shelf fields per worksheet
• twb_sheet_filters(): categorical members, range min/max, include/exclude mode
• twb_sheet_axes(): reversed, include-zero, scale-type per axis rule
• twb_sheet_sorts(): sort direction and method per worksheet

Phase 3 — Per-dashboard intelligence (R/dashboard_details.R):

• twb_dashboard_sheets(): sheets on a dashboard with zone pixel positions
• twb_dashboard_layout(): full zone tree with parent IDs and component types
• twb_dashboard_actions(): filter and URL actions with source/target/trigger/url

All 7 new functions wired into TwbParser R6 methods and active bindings. globals.R updated with all new NSE column names.

Tests: test-cleaners.R, test-graph-bugs.R, test-sheet-details.R,
test-dashboard-details.R (114 new assertions, all passing).

Docs: NEWS.md, README.md, cran-comments.md, _pkgdown.yml, vignette updated.
R CMD check: 0 errors | 0 warnings | 0 notes.

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