refactor: rename environment to workspace

[Adam-D-Lewis]

Summary

• Mechanical rename of all "environment" references to "workspace" across the entire codebase
• No functional changes — purely a terminology alignment to better reflect the domain model
• 70 files changed, 2539 insertions(+), 2539 deletions(-)

What's renamed

• Backend models: Environment → Workspace, EnvironmentVersion → WorkspaceVersion, EnvironmentTag → WorkspaceTag
• API routes: /environments → /workspaces
• Handlers: EnvironmentHandler → WorkspaceHandler
• RBAC: env: prefix → ws: prefix
• Executor interface: CreateEnvironment → CreateWorkspace, etc.
• Audit constants: ActionCreateEnvironment → ActionCreateWorkspace, etc.
• CLI client: all environment types and methods → workspace equivalents
• CLI commands: help text, variable names, error messages
• Frontend: types, API layer, React Query hooks, pages, components, navigation
• Wails desktop bindings: Environment → WailsWorkspace
• Swagger/OpenAPI docs: regenerated with new type names

Test plan

• go vet ./... passes
• go test ./... — all tests pass
• npx tsc --noEmit — no TypeScript errors
• npm run build — frontend production build succeeds

[Adam-D-Lewis]

closes #77
related to #78