feat : add alias support for new participant syntax

[omkarht]

📑 Summary

This PR adds comprehensive alias support for participants in Sequence Diagrams, enabling users to define aliases in two ways:

1. External Alias Syntax (using as keyword): Combine participant stereotypes with aliases using syntax like participant API@{ "type" : "boundary" } as Public API
2. Inline Alias Syntax (inside config object): Define aliases directly in the configuration object like participant API@{ "type": "boundary", "alias": "Public API" }

Both syntaxes allow users to assign UML stereotype types and descriptive aliases to participants, with full backward compatibility maintained.

🎯 Key Features

1. External Alias Syntax

Users can now use the as keyword after stereotype configuration:

sequenceDiagram-+
  participant API@{ "type" : "boundary" } as Public API
  actor DB@{ "type" : "database" } as User Database
  participant Svc@{ "type" : "control" } as Auth Service

  API ->> Svc: Authenticate
  Svc ->> DB: Query user
  DB -->> Svc: User data
  Svc -->> API: Token

2. Inline Alias Syntax

Users can define aliases directly inside the configuration object:

sequenceDiagram
  participant API@{ "type": "boundary", "alias": "Public API" }
  participant Auth@{ "type": "control", "alias": "Auth Service" }
  participant DB@{ "type": "database", "alias": "User Database" }
  
  API->>Auth: Login request
  Auth->>DB: Query user
  DB-->>Auth: User data
  Auth-->>API: Access token

3. Precedence Rule

When both inline and external aliases are provided, the external alias takes precedence:

sequenceDiagram
  participant API@{ "type": "boundary", "alias": "Internal Name" } as External Name
  [ # Will display as "External Name"]

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🦋 Changeset detected

Latest commit: b33ce14

The changes in this PR will be included in the next version bump.

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❌ Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 3.55%. Comparing base (6b9f26d) to head (b33ce14).

Files with missing lines	Patch %	Lines
...ckages/mermaid/src/diagrams/sequence/sequenceDb.ts	0.00%	3 Missing ⚠️

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@@            Coverage Diff             @@
##           develop   #7136      +/-   ##
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- Coverage     3.55%   3.55%   -0.01%     
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  Files          473     474       +1     
  Lines        47496   47510      +14     
  Branches       731     731              
==========================================
  Hits          1687    1687              
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Files with missing lines	Coverage Δ
packages/mermaid/src/types.ts	100.00% <ø> (ø)
...ckages/mermaid/src/diagrams/sequence/sequenceDb.ts	0.00% <0.00%> (ø)

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Build	Status	Details	Updated (UTC)
default (Inspect)	⚠️ Changes detected (Review)	10 added	Nov 14, 2025, 7:08 AM

[sidharthv96]

I'm not sure if we should support this syntax. The @{ } syntax is meant to define all custom properties of a node. So shouldn't it just be ID@{ alias: 'Alias' }?

Mixing the old syntax with new seems wrong.