Standardize Settings parameter position: always pass as first argument

[aram356]

Summary

Standardize function signatures so that Settings (or &Settings) is always the first parameter when present. Currently the position varies across the codebase.

Current State

Function	Settings Position	File
enforce_basic_auth(settings, req)	First ✓	crates/common/src/auth.rs:9
generate_synthetic_id(settings, req)	First ✓	crates/common/src/synthetic.rs:30
encode_url(settings, plaintext_url)	First ✓	crates/common/src/http_util.rs:47
decode_url(settings, token)	First ✓	crates/common/src/http_util.rs:74
proxy_request(settings, req, config)	First ✓	crates/common/src/proxy.rs:303
rewrite_creative_html(body, settings)	Last ✗	crates/common/src/creative.rs
serve_static_with_etag(body, req, content_type)	Not present	crates/common/src/http_util.rs:11

Target State

All functions that accept Settings should have it as the first parameter:

// Before
fn rewrite_creative_html(body: &str, settings: &Settings) -> Result<String, Error>

// After  
fn rewrite_creative_html(settings: &Settings, body: &str) -> Result<String, Error>

Rationale

• Consistency - Easier to read and understand function signatures
• Convention - Follows common Rust patterns where context/config comes first
• Discoverability - When scanning code, settings parameter is always in the same place

Changes Required

1. Identify all functions with Settings parameter not in first position
2. Update function signatures to move Settings to first position
3. Update all call sites to match new signatures
4. Run tests to ensure no regressions

Files to audit

• crates/common/src/creative.rs
• crates/common/src/html_processor.rs
• crates/common/src/integrations/*.rs

Testing

1. cargo build - Ensure compilation succeeds
2. cargo test - Ensure all tests pass
3. cargo clippy - No new warnings

Complexity

Low - Mechanical refactoring with IDE support

Labels

• good first issue
• tech-debt
• refactoring