Forge: fall back to the run jar when there is no @args launcher (#42)

[CaYatur]

Closes #42. Part of the provider-reliability pass (#44).

Problem

Creating a Forge server failed with installer-args-not-found on pre-1.17 versions. After the installer runs, createServer only looked for an OS @args file (win_args.txt / unix_args.txt), which is emitted by Forge 1.17+ / NeoForge only. Older Forge (≤ 1.16.5) instead produces a runnable server jar, so the lookup returned null and creation always failed even though the install succeeded.

Fix

• New pure, unit-testable pickForgeRunJar() in serverDetect.ts: given the top-level jar listing, pick the produced forge/neoforge run jar (a -universal.jar on ≤ 1.12, forge-<mcver>-<forgever>.jar on 1.13–1.16), skipping the installer jar itself and never a plain vanilla minecraft_server.*.jar.
• createServer: if no @args file is found after the installer runs, fall back to launching that jar with -jar; only throw installer-args-not-found when neither an args file nor a run jar exists. 1.17+ Forge / NeoForge keep the @args path unchanged.
• The -universal-first ordering is correct only because listJars is top-level only (on 1.13–1.16 a -universal.jar exists but under libraries/, so it must stay out of scope). Documented in a comment so it isn't made recursive.

Verify — and its limits

• typecheck, build — pass.
• MSMS_SMOKE_WIZARD PASS, including a new block that exercises the jar-vs-args decision: universal (≤1.12) / loader jar (1.13–1.16) / none (1.17+ installer-only) / installer excluded / vanilla jar never picked / neoforge keyword.
• Honesty note: the smoke tests the selection logic against the filename shapes from the issue spec + Forge docs — it does not run the real installer (old Forge needs a JDK 8 toolchain not available here). The 1.16.5 run-jar name (forge-<mcver>-<forgever>.jar) was cross-checked against Forge community docs.
• Scope: this resolves the installer-args-not-found failure only. Actually launching an old-Forge server additionally needs a compatible JRE (Java 8) — that is the Java-provisioning / hardening-matrix concern (Harden server creation across the whole version/loader matrix (umbrella) #44), not this change.

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