A help add-in for the IDE, impexp in process for the harness, and WIP notes without their history

[KubaO]

Adds an IDE add-in that opens the documentation for the name under the cursor, makes the harness pack and unpack projects in process, and removes the history from the WIP.*.md notes.

The add-in is a work in progress. I don't suggest trying to use it yet.

• help add-in (add-in/, new): F1 opens the page for the selection or the name at the cursor, in a TWINBASIC HELP pane with search. It asks the compiler's hover where the name is declared, so that c.Add finds Collection.Add, and for a name with no page shows its declaration and [Description]. A new addin-test.bat lane tests it, and try-help-addin.bat opens an IDE with it to try by hand.
• site, build: the pane's pages follow the IDE's theme and drop the sidebar and header, through ?theme=light|dark and ?pane=1, kept in sessionStorage and never in the reader's stored choice. A local build rewrites the add-in's committed copy of tB/symbols.json when it differs; CI and --serve only say so.
• harness:
  • The tools pack and unpack projects with impexp.mjs in process, not with the compiler's import and export, so a project that embeds a package stages (import exits 999 for one: Export / Import should not include packages twinbasic#841).
  • Lane runners claim the first free DevTools ports with lock files. test/ports.test.mjs is a new step in test.bat and CI (21 now).
  • bug_repro vb6 and vb6run report an exe that the event log says faulted, because a faulting VB6 exe exits 0.
• bugs, docs: four COM entries gain a VB6 project, 18 in all. VB6 repeats a CallByName after DISP_E_MEMBERNOTFOUND as twinBASIC does, so that entry is retired and its WARNING in IDispatch.md becomes a NOTE. VB6 also returns E_NOINTERFACE from Advise for a sink without the outgoing interface, so the Unadvise entry narrows to the bad cookie. New, filed as A member's [Description] is listed as a member of its enum in the hover, and is not shown on the member twinbasic#2465: an enum member's [Description] is listed as a member in the hover, and not shown on the member.
• WIP notes: the history is dropped and WIP.OldJekyll.md removed: the notes go from 9,571 lines to 8,346. WIP.md says where a note belongs, and that sessions use gh read-only.

addin-test.bat, try-help-addin.bat, bug_repro vb6 and vb6run need a twinBASIC install or VB6, so they stay outside every gate and CI.