Build tooling work, commits C76-C84: smaller builder and harness modules, two render and date fixes

[KubaO]

Continues the tooling review: it splits three large builder and harness files into modules and fixes two small defects that the splits exposed.

• render: the ellipsis plugin counts each run of dots where it sits, rather than counting across the whole text. test/render.test.mjs (new) covers it. The toc marker's comment is corrected, and the C76 split was not taken.
• builder: builder/gantt.mjs (new) holds the Gantt sections and their grouping, moved out of tbdocs.mjs.
• builder: builder/strftime.mjs (new) holds the date formatter, moved out of template.mjs. Its %j now gives the calendar day in three digits. No build calls formatDate, because no page sets last_modified_date. test/strftime.test.mjs (new) covers it.
• builder: book.mjs's image-path helpers move next to their one caller.
• scripts: scripts/lib/example-batches.mjs (new) holds check_examples' batching, canaries and fence classifier, and check_examples.mjs shrinks by about 1,100 lines. test/example-batches.test.mjs (new) tests it with no IDE.
• scripts: tb-ide.mjs sheds its console reading (tb-ide-console.mjs) and its add-in introspection (tb-ide-addins.mjs). launchIde's refusal now names the process that holds the port.
• test.bat: runs the three new node --test files. They are also added to the shared CI action, and check_gate_lists is updated to match.
• docs: Phase 4's Landed entries in builder/PLAN-TOOLING-REVIEW.md are cut to what later work needs, and the WIP notes are updated.