Add wch/ vendor tree: datasheets + reference manuals for CH32V003/V006/V103/V203/V208/V30x/X035/L103 + WCH-Link

[zackees]

Gap: this repo has no WCH content at all (verified 2026-07-21 — no wch/ vendor dir, zero ch32* files in the tree), while FastLED/fbuild now builds nine CH32V families and its audits have to cite scattered web mirrors instead of pinned documents.

Request

Add a wch/ vendor tree following the existing espressif/soc/* layout:

wch/mcu/CH32V003/   datasheet.pdf + reference-manual.pdf + SOURCES.md
wch/mcu/CH32V006/   (CH32V005/006/007 + CH32M007 family docs)
wch/mcu/CH32V103/
wch/mcu/CH32V203/   (V20x DS covers 203/208; RM is CH32FV2x_V3x)
wch/mcu/CH32V208/
wch/mcu/CH32V30x/   (V303/305/307)
wch/mcu/CH32X035/
wch/mcu/CH32L103/
wch/probe/WCH-Link/ WCH-LinkUserManual.pdf + SOURCES.md

PDFs from wch-ic.com product pages (English versions); SOURCES.md records the exact URL + retrieval date + document version, per repo convention.

Why now

The 2026-07-21 CH32V bench-readiness sweep in FastLED/fbuild had to verify chip facts (flash/RAM maps, bootloader presence and entry: e.g. CH32V003 has no USB and a software-entry-only UART bootloader; X035 ISP entry is PC16/PC17 at power-on, not BOOT0) against third-party mirrors (akizukidenshi.com PDF mirrors, Olimex's WCH-LinkUserManual copy). Those facts now back board JSON data and the upcoming wlink/wchisp deployers in fbuild — they should be citable against pinned in-repo documents. This was also flagged as the "stretch" item in FastLED/fbuild#1102 (sub-item #1109).

The FastLED/fbuild CH32V meta issue (2026-07-21 sweep) links here.

[zackees]

Parent meta: FastLED/fbuild#1130 (2026-07-21 CH32V bench-readiness sweep).

[zackees]

Source manifests for all requested CH32 families and WCH-Link are merged in #7. The binary PDFs remain outstanding because the repository uses Git LFS and the current checkout could not complete the existing LFS transfer; leaving this issue open until those payloads are uploaded.