Tool AGS refactor

[eliknebel]

Implements the Tool AGS feature plan (docs/features/tool-ags/plan.md) through Phases 0–3 with new typed AGS APIs, structured errors, scope enforcement, telemetry, compatibility hooks, docs, and tests. This PR also removes legacy AGS compatibility helpers to simplify the API surface.

What’s Included

Tool AGS 2.0 implementation

Refactored Lti_1p3.Tool.Services.AGS into modular components:

• Endpoint, Page, Result typed structs
• Parser for claim/payload parsing
• ScopePolicy for per-operation scope preflight
• Client for HTTP request/retry handling
• Errors for normalized error maps
• Telemetry for AGS events
• CompatibilityPolicy for LMS behavior overrides

Added/updated AGS public operations:

• from_launch_claim/1
• list_line_items/3
• read_line_item/4
• create_line_item/4
• update_line_item/5
• delete_line_item/4
• post_score/5
• list_results/4
• fetch_all_results/4
• required_scopes/1

Removed legacy AGS helpers:

• post_score/3
• fetch_line_items/2
• create_line_item/5
• update_line_item/3
• fetch_or_create_line_item/5
• grade_passback_enabled?/1
• get_line_items_url/2
• has_scope?/2
• required_scopes/0

Shared utility extraction

• Added Lti_1p3.Services.HTTP.Request for shared bearer-header/path helpers.
• Reused in AGS and NRPS clients.

Filter/pagination support improvements

• Extended Lti_1p3.Services.HTTP.QueryFilters to support AGS filter keys (resource_id, tag, user_id).

Documentation and feature artifacts

Added:

• docs/tool_ags_guide.md
• docs/features/tool-ags/requirements_matrix.md
• docs/features/tool-ags/utility_extraction.md
• docs/features/tool-ags/qa_report.md

Updated:

• docs/features/tool-ags/plan.md checkboxes for Phases 0–3
• README.md
• docs/telemetry.md
• CHANGELOG.md
• mix.exs docs extras

Tests

Reworked AGS tests for:

• parser/scope/error branches
• line item CRUD
• score posting
• results pagination + traversal
• telemetry events

Also:

• Added shared utility tests for Lti_1p3.Services.HTTP.Request
• Extended QueryFilters tests for AGS keys
• Updated deprecated NRPS legacy test callsite to avoid compile-time deprecation warning noise in test output
• Removed AGS legacy compatibility behavior tests (since legacy API was removed)

Notes

• Phase 4 (manual LMS sandbox interoperability) is documented in docs/features/tool-ags/qa_report.md and remains
  pending external sandbox execution.