fix: replace SAC with SEP-41 terminology

[marcelosalloum]

What

Replace generic "SAC" references with "SEP-41" across documentation, comments, error messages, and internal function names. Constant names (USDC_SAC_*, XLM_SAC_*, SAC_ADDRESSES) are preserved since they identify specific SAC contract addresses.

Why

SAC (Stellar Asset Contract) is only a subset of SEP-41 tokens. MPP supports all SEP-41-compliant tokens, not just SACs. Using "SAC" generically misrepresents the SDK's capabilities.

Changes across 13 files

• Docs (README.md, CLAUDE.md, CHANGELOG.md, demo/README.md): "SAC token transfers" → "SEP-41 token transfers"
• Diagrams (charge-flow.md, mindmap.md): updated flow labels and function references
• Source (Methods.ts, client/Charge.ts, server/Charge.ts): docstrings, comments, error message
• Constants (constants.ts): JSDoc comments now say "SEP-41 token contract (SAC)"
• Internal functions: verifySacInvocation → verifyTokenInvocation, verifySacTransfer → verifyTokenTransfer
• Tests (Charge.test.ts): error message assertions updated to match

[Copilot]

Pull request overview

Replaces generic “SAC” terminology with “SEP-41” across the SDK and documentation to more accurately describe support for SEP-41-compliant token transfers (while preserving SAC-specific constant names for well-known contract addresses).

Changes:

• Updated docs/diagrams/examples to refer to “SEP-41 transfer” rather than “SAC transfer”.
• Renamed internal verification helpers in the charge server from verifySac* to verifyToken* and updated the corresponding error message.
• Updated server charge tests to assert the new error message wording.

Reviewed changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
sdk/src/constants.ts	Updates JSDoc/comments to describe SAC addresses as SEP-41 token contracts.
sdk/src/charge/server/Charge.ts	Renames internal verification helpers and updates SEP-41 wording in docs/error message.
sdk/src/charge/server/Charge.test.ts	Updates error-message assertions for renamed/rewritten verification error text.
sdk/src/charge/Methods.ts	Updates method/schema documentation from SAC to SEP-41.
sdk/src/charge/client/Charge.ts	Updates client docstring and inline comment to SEP-41 terminology.
README.md	Updates public documentation wording and parameter descriptions to SEP-41 terminology.
examples/charge-server.ts	Updates example header comment to SEP-41 terminology.
examples/charge-client.ts	Updates example header comment to SEP-41 terminology.
diagrams/mindmap.md	Updates diagram references to new internal helper names.
diagrams/charge-flow.md	Updates flow title/labels and helper names to SEP-41 terminology.
demo/README.md	Updates demo documentation labels to SEP-41 terminology.
CLAUDE.md	Updates repo guidance to SEP-41 terminology where applicable.
CHANGELOG.md	Adds an Unreleased entry and updates historical wording to SEP-41 terminology.

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