fix(project): resolve -e/--env for all Admin-API commands

[Lena (moshimorschi)]

What changed?

All project commands that talk to a shop now resolve the target environment from -e/--env, matching the executor-based commands. Previously only executor commands (admin-build, ci, dev, ...) honored the flag; the Admin-API commands built their client from the base config and ignored it.

Behavior with the issue's config (base URL port 9, environments.staging port 29):

Command	Before	After
extension list -e staging	contacts base (port 9)	contacts staging (port 29)
extension uninstall -e staging Foo	contacts base (port 9)	contacts staging (port 29)
extension list -e nonexistent	silently contacts base	fails: environment "nonexistent" not found in config
extension list (no -e)	contacts base	contacts base (unchanged)

Why?

-e staging silently targeting the default environment means a mutating command such as extension uninstall -e staging MyPlugin could act on the wrong, possibly production, shop, and environment-name typos passed silently. See #1226 for the full analysis.

How was this tested?

• New Config.WithEnvironment unit tests (override, base fallback, unknown-name error, no-op when no environments, no mutation of the original config).
• list end-to-end tests asserting -e staging contacts the staging URL and -e nonexistent is rejected.
• A table-driven test running all 12 Admin-API commands, each asserting it rejects an unknown environment and contacts the selected environment's URL. Verified failing against the pre-fix code and passing with the fix.
• Full go test ./... passes; gofmt and go vet clean.

Related issue or discussion

Fixes #1226

[Codecov Comments Bot (codecov-commenter)]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 54.22%. Comparing base (3eaa8af) to head (0c89454).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1257      +/-   ##
==========================================
+ Coverage   53.46%   54.22%   +0.75%     
==========================================
  Files         303      303              
  Lines       23322    23342      +20     
==========================================
+ Hits        12470    12657     +187     
+ Misses      10848    10644     -204     
- Partials        4       41      +37     

Flag	Coverage Δ
go-test	54.22% <100.00%> (+0.75%)	⬆️

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