Bump Semantic Kernel to 1.74.0 and update deps

[MarioEncamina]

Description

Add project guidelines and markdownlint config, bump VersionPrefix to 10.0.3 and add CHANGELOG entry for 10.0.3. Update Semantic Kernel dependencies to 1.74.0 (Core, Abstractions, Connectors.AzureOpenAI, Plugins.Document => 1.74.0-alpha, Plugins.Memory => 1.74.0-alpha, AzureAISearch/Qdrant => 1.74.0-preview) across multiple projects and sample. Also update related package versions (Microsoft.Extensions.DependencyInjection.Abstractions -> 10.0.4, Microsoft.Extensions.Options -> 10.0.2) and perform formatting/cleanup in CHANGELOG.md.

Type of change

Please check only those options that are relevant with a (✅).

• The code builds clean without any errors or warnings
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist

Please check all options from this checklist when validating your pull request with a (✅).

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules
• I didn't break anyone 😄

[Copilot]

Pull request overview

This PR updates the repo’s Semantic Kernel dependency set (and a couple of related Microsoft.Extensions.* packages), bumps the library version to 10.0.3, and adds supporting repository guidelines/lint configuration.

Changes:

• Bump Semantic Kernel packages across several projects to 1.74.0 (including -alpha/-preview SK packages where applicable).
• Update VersionPrefix to 10.0.3 and add a 10.0.3 entry in CHANGELOG.md (plus formatting cleanup).
• Add .github/copilot-instructions.md project guidelines and a .markdownlint.json configuration.

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/Encamina.Enmarcha.SemanticKernel.Plugins.QuestionAnswering/Encamina.Enmarcha.SemanticKernel.Plugins.QuestionAnswering.csproj	Bumps Microsoft.SemanticKernel.Abstractions to 1.74.0.
src/Encamina.Enmarcha.SemanticKernel.Plugins.Memory/Encamina.Enmarcha.SemanticKernel.Plugins.Memory.csproj	Bumps Microsoft.SemanticKernel.Abstractions to 1.74.0.
src/Encamina.Enmarcha.SemanticKernel.Plugins.Chat/Encamina.Enmarcha.SemanticKernel.Plugins.Chat.csproj	Bumps SK abstractions and Microsoft.Extensions.Options.
src/Encamina.Enmarcha.SemanticKernel.Connectors.Memory/Encamina.Enmarcha.SemanticKernel.Connectors.Memory.csproj	Bumps SK memory connector packages and DI abstractions.
src/Encamina.Enmarcha.SemanticKernel.Connectors.Document/Encamina.Enmarcha.SemanticKernel.Connectors.Document.csproj	Bumps SK Azure OpenAI connector and Document plugin packages.
src/Encamina.Enmarcha.SemanticKernel.Abstractions/Encamina.Enmarcha.SemanticKernel.Abstractions.csproj	Bumps SK Core and Azure OpenAI connector dependencies.
src/Encamina.Enmarcha.Agents/Encamina.Enmarcha.Agents.csproj	Bumps Microsoft.SemanticKernel meta-package to 1.74.0.
samples/SemanticKernel/Encamina.Enmarcha.Samples.SemanticKernel.QuestionAnswering/Encamina.Enmarcha.Samples.SemanticKernel.QuestionAnswering.csproj	Bumps SK Memory plugin package to 1.74.0-alpha.
Directory.Build.props	Updates VersionPrefix to 10.0.3.
CHANGELOG.md	Adds 10.0.3 entry and normalizes markdown formatting.
.markdownlint.json	Adds markdownlint configuration.
.github/copilot-instructions.md	Adds repo/project guidelines for Copilot usage and contributor conventions.

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