feat: add pluggable auth system

[flossypurse]

Summary

• add a pluggable authentication package with basic/JWT support plus helpers and tests
• integrate the new authenticator across HTTP and poll subsystems and expose listener helpers
• wire bearer token support through the CLI clients and API tests

Testing

• go test ./...

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https://chatgpt.com/codex/tasks/task_b_68f7b95f9458832bb26392f5bd205d19

[codecov]

Codecov Report

❌ Patch coverage is 62.06897% with 99 lines in your changes missing coverage. Please review.
✅ Project coverage is 50.17%. Comparing base (30c3272) to head (7688c7d).

Files with missing lines	Patch %	Lines
internal/app/auth/auth.go	66.49%	50 Missing and 14 partials ⚠️
internal/app/plugins/poll/poll.go	72.72%	4 Missing and 2 partials ⚠️
internal/app/subsystems/api/http/http.go	64.70%	4 Missing and 2 partials ⚠️
cmd/invoke/invoke.go	0.00%	5 Missing ⚠️
cmd/promises/promises.go	0.00%	5 Missing ⚠️
cmd/schedules/schedules.go	0.00%	5 Missing ⚠️
cmd/tasks/tasks.go	0.00%	5 Missing ⚠️
internal/app/subsystems/api/grpc/grpc.go	72.72%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #885      +/-   ##
==========================================
+ Coverage   49.92%   50.17%   +0.25%     
==========================================
  Files         126      127       +1     
  Lines       14487    14722     +235     
==========================================
+ Hits         7232     7387     +155     
- Misses       6773     6838      +65     
- Partials      482      497      +15     

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