wiki: add Archive Mode page; drop xdelta3; refresh CLI ref + features
Updates to reflect the 2026-04 archive-mode landing and the 2026-05
xdelta3 removal.
Page-level changes:
* New: Archive-Mode.md — full reference for the Steam archive-mode
pipeline: login, project file (.xarchive), single-pass and
polling downloads, max-retries / restart-delay semantics,
SessionDead recovery + outage alert path, crack pipeline, MultiUp +
PrivateBin upload, BBCode template editor with forum-rendered
preview toggle, Telegram + Discord notifications, archive depot
historical-build pulls, GUI overview.
* Sidebar: add Archive-Mode entry between Repack-Mode and
Engines-and-Presets.
* Home: list all three modes; mention archive workflow in quick-start.
* Installation: drop xdelta3 from prebuilt binaries list; document
the optional 'archive' extra.
* Features: split into Update Patch / Repack / Archive / Shared
sections. Archive section enumerates polling + outage recovery +
upload + BBCode + notify + historical-pull surface. Drop xdelta3
from the engine count.
* CLI-Reference: drop xdelta3 from --engine choices; add 'archive'
subcommand summary that links to Archive-Mode for the full flag set.
* Engines-and-Presets: drop xdelta3 section + table; rewrite engine
recommendation matrix. Note that bzip2 presets need the FULL
hdiffpatch stub (auto-selected by exe_packager).
* Output-Formats: PFMD container is now JojoDiff-only; HDiffPatch
uses its native upstream container.
* Stub-System: drop xdelta3 stub variants from the prebuilt list and
the make-target list. Update directory tree to reflect the
src/core/archive/ subtree, the GUI archive_*.py modules, and
path_safe.h.
Split into per-topic pages with sidebar navigation
Populate Home page from README