docs: move design/roadmap docs to the wiki, trim the repo root

The repository root carried 11 large Markdown files (~330 KB); most were
long-lived design records rather than things a newcomer needs on first
contact, which buried the README and mixed "how to use Ludic" with "how we
decided to build it."

Move the design/roadmap docs to the Forgejo wiki (now enabled and
populated): Events, Networking, Scenes, Lifecycle, Mobile and
Syntax-redesign design records, the Bootstrap deep-dive and the Luanti
roadmap, under a Home index + sidebar. Each page had its selfhost/ source
links corrected for the #29 reorg and every repo-relative link rewritten to
an absolute URL on main so it resolves from the wiki.

All eight were current, actively-maintained records, so none were dropped.
The root now holds README.md plus the two user-facing references,
LANGUAGE.md and COMPILING.md; the README links to the wiki, and the
remaining references in LANGUAGE.md / COMPILING.md / examples/README.md and
the emit_net.ludic header comment point at the wiki pages. The emit_net.ludic
change is a comment only — the seed stays byte-identical and bootstrap-cfree
+ the full suite (56) stay green.

Closes #26

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

COMPILING.md

@@ -10,7 +10,7 @@
 > convenience wrapper over the compiler. `--fmt` is reimplemented as a lex+parse
 > gate (the doc-check hook). The `--target`/cross-compile and `--shared` paths are
 > still features of the old C driver not yet re-implemented on the self-hosted
-> toolchain. See BOOTSTRAP.md §5.7.
+> toolchain. See the [Bootstrap deep-dive](https://git.workshopsoft.io/workshopsoft/ludic/wiki/Bootstrap) §5.7 on the wiki.
 >
 > From a clean checkout, build the compiler and the task-runner in one line, then
 > let `bin/x` do the rest (run it from the repository root):