fix(ch32v): main fails to compile - adjacent string literals in validate_ch32v_framework format! (#1114 regression)

[zackees]

Severity: CRITICAL — main does not compile. Blocks every other bench fix.

Problem

validate_ch32v_framework in crates/fbuild-build-mcu/src/ch32v/orchestrator.rs:257-260 contains two adjacent string literals inside format!:

Some(other) => Err(fbuild_core::FbuildError::ConfigError(format!(
 "ch32v: framework = {other} is not supported yet; only `framework = arduino` "
 "builds today (FastLED/fbuild#1108)"
))),

Rust has no implicit adjacent-literal concatenation — this is a syntax error. Introduced by PR #1114 (commit df6901c).

Evidence (verified)

• soldr cargo check -p fbuild-build-mcu on main @ 69b51cf fails with error: expected `,`, found `"builds today (FastLED/fbuild#1108)"` at orchestrator.rs:259.
• CI on main is red: Check Windows (run 29878684396) and Check macOS (run 29878684443) both failed on the fix(ch32v): clean up board data and dead linker code #1116 push.

Fix

Merge into one literal (or use concat!). One line. Add the missing space handling: the current text ends the first fragment with a trailing space, so the joined message should read ...only \framework = arduino` builds today (#1108)`.

Acceptance

• soldr cargo check --workspace --all-targets passes.
• The fix(ch32v): validate framework selection #1114 unit tests for validate_ch32v_framework (message contains 1108) pass.
• Check Windows/macOS/Ubuntu green on main.

Found during the 2026-07-21 CH32V bench-readiness sweep.

[zackees]

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