Add README install.sh docs, bump SemVer to 1.0.4, add DeveloperGuide.md.
- README.md: add an Installation section (right after the intro) summarizing
install.sh usage/options, so new readers see it first.
- internal/version/version.go: bump SemVer 1.0.3 -> 1.0.4.
- docs/DeveloperGuide.md (new): required tooling, Makefile build/test/release
targets, how/when to bump SemVer, dev -> main -> release stream
promotion/merge workflow, and why ai/ + bin/ are isolated stream paths.