docs: document Go versions for rules

[ColumbusLabs]

Motivation

The available-rules table currently does not show which target Go versions each rule applies to. This makes version-gated rules difficult to identify without reading their implementations or individual descriptions.

Changes

• add a Go version column covering all 104 registered rules
• document minimum, maximum, and behavior-change versions from the rule implementations
• add the missing multiline-if-init table row so the table matches the rule registry
• explain Any and target-version semantics below the table
• refresh the generated README table of contents for the existing MegaLinter section

Verification

• npx --yes markdownlint-cli2@0.22.0 .
• npx --yes markdown-toc@1.2.0 --maxdepth 4 --no-first1 --bullets "-" -i README.md (idempotent)
• npx --yes markdown-toc@1.2.0 --maxdepth 2 --no-first1 --bullets "-" -i RULES_DESCRIPTIONS.md (idempotent)
• git diff --check
• verified all 104 README rows exactly match the 104 rule-description headings

make all and mdsf verify . were not run locally because Go and the configured embedded-code formatters are not installed in this environment; GitHub Actions will exercise the repository-wide checks.

Closes #1311