fix(environment): give DEV an identity color

[HandSonic]

Related issue

N/A — contract gap found by reviewing 14729e0 (identity colors); described below.

Summary

SysEnvironmentServiceImpl defines colors for TEST (GREEN) and RELEASE (RED) but DEV shipped with none: /api/common/environment/list_all returns color: null for DEV while the client types Environment.color as non-null and uses it directly for badge styling (current consumers happen to guard; any new consumer calling .color.toLocaleLowerCase() throws). DEV now carries BLUE, and a test pins that every environment defines a non-blank color.

Affected surfaces

• Frontend / Web
• Backend / API / Storage
• Database plugin / Driver
• JCEF / Desktop packaging
• CI / Build / Release
• Documentation only

Verification

• mvn -pl chat2db-community-domain/chat2db-community-domain-core -am test -Dmaven.test.skip=false -Dtest=SysEnvironmentServiceImplTest: 2/2 green (incl. new everyEnvironmentCarriesAnIdentityColor).
• Fork CI green: fix(environment): give DEV an identity color HandSonic/Chat2DB#42.

Risk and compatibility

• Public API or stored data: N/A (computed list, nothing persisted).
• Database or driver compatibility: N/A.
• Network, privacy, or security: N/A.
• Community / Local / Pro boundary: N/A.
• Backward compatibility: null → BLUE only adds information.

Reviewer map

• Start here: SysEnvironmentServiceImpl DEV constant.
• Failure condition: none.
• Rollback or disable path: revert single commit.

Contributor declaration

• I linked the Issue that defines this change.
• I tested the affected behavior and reported the actual results above.
• I did not include credentials, private data, or generated build output.
• I disclosed substantial AI assistance below, or this PR contains no substantial AI-generated code.

AI assistance: substantial — fix and tests drafted with AI assistance, verified locally.