dev: add devcontainers setup

[qboileau]

Add alternative to Nix to setup dev environment with devcontainers that reuse nix to setup dev environment.

[github-actions]

Container image CVE report

base-jre-25

Scanner	Critical	Critical+High	Total
Trivy	✅ 0	✅ 0	0
Grype	✅ 0	⚠️ 3	3

Grype critical+high by component

Component	Findings
libcrypto3 3.6.3-r4	1
libssl3 3.6.3-r4	1
openssl 3.6.3-r4	1

base-monitoring

Scanner	Critical	Critical+High	Total
Trivy	✅ 0	✅ 0	0
Grype	✅ 0	⚠️ 3	7

Grype critical+high by component

Component	Findings
libcrypto3 3.6.3-r4	1
libssl3 3.6.3-r4	1
openssl 3.6.3-r4	1

base-os

Scanner	Critical	Critical+High	Total
Trivy	✅ 0	✅ 0	0
Grype	✅ 0	✅ 0	0

debug

Scanner	Critical	Critical+High	Total
Trivy	✅ 0	✅ 0	0
Grype	✅ 0	⚠️ 17	35

Grype critical+high by component

Component	Findings
stdlib go1.25.12	6
jackson-databind 2.21.2	2
jline-remote-telnet 3.30.4	2
golang.org/x/net v0.55.0	1
golang.org/x/text v0.37.0	1
jackson-core 2.21.2	1
jetty-security 12.0.34	1
libcrypto3 3.6.3-r4	1

_{Trivy counts fixed vulnerabilities only; Grype includes unfixed, so its totals run higher. Full reports are in the workflow artifacts.}