Implement cookie handling with SameSite support and validation.

[gustavofreze]

No description provided.

[Copilot]

Pull request overview

Adds first-class Set-Cookie support to the TinyBlocks HTTP response model, including SameSite handling and cookie name/value validation, while improving response header composition to support multi-value headers like Set-Cookie.

Changes:

• Introduces Cookie and SameSite public APIs and internal validation/value objects for RFC-oriented cookie name/value constraints.
• Updates internal response header aggregation to preserve multiple header values (enabling multiple Set-Cookie headers) and adds tests around case-insensitive header operations.
• Documents cookie usage patterns in the README and adds dedicated PHPUnit coverage for cookie serialization and invariants.

Reviewed changes

Copilot reviewed 22 out of 22 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
tests/SameSiteTest.php	Verifies SameSite enum backed values match Set-Cookie casing.
tests/ResponseWithCookiesTest.php	Ensures responses preserve one or multiple Set-Cookie values and coexist with other headers.
tests/HeadersTest.php	Adds coverage for withAddedHeader(), case-insensitive header operations, and header merging behavior.
tests/CookieTest.php	Covers cookie serialization order, immutability, expires formatting, and invariant exceptions.
src/SameSite.php	Adds SameSite backed enum for cookie attribute rendering.
src/Cookie.php	Implements an immutable Cookie header value object with fluent builders and serialization.
src/Internal/Cookies/CookieName.php	Adds cookie name validation and string conversion.
src/Internal/Cookies/CookieValue.php	Adds cookie value validation and string conversion.
src/Internal/Exceptions/*.php	Introduces specific exceptions for invalid cookies and invariant violations.
src/Internal/Response/ResponseHeaders.php	Changes header merging and adds case-insensitive header lookup/add/replace/remove helpers.
src/Internal/Response/InternalResponse.php	Fixes header mutation methods to operate on existing headers instead of replacing them.
README.md	Documents cookie creation, multiple cookies, expiration, expires usage, and SameSite rules.
.github/copilot-instructions.md	Adds repository-specific Copilot task guidance.
.claude/CLAUDE.md	Adds project workflow/testing command guidance.
.claude/rules/*.md	Adds Claude rule files for testing, domain modeling, code style, docs, and workflows.