docs(dllm): align DiffusionGemma guides with the SFT recipe (#3550)

* docs(dllm): align DiffusionGemma guides with the SFT recipe

Document the recipe's one-canvas-per-step loss, encoder AR term, LoRA targets, and generation-tag chat template, and keep the GitHub .md in sync with the Fern .mdx.

Signed-off-by: Kashif Rasul <kashif.rasul@gmail.com>

* Update docs/guides/dllm/diffusiongemma.md

Co-authored-by: jgerh <163925524+jgerh@users.noreply.github.com>

* Update docs/guides/dllm/diffusiongemma.md

Co-authored-by: jgerh <163925524+jgerh@users.noreply.github.com>

* Update docs/guides/dllm/diffusiongemma.md

Co-authored-by: jgerh <163925524+jgerh@users.noreply.github.com>

* Update docs/guides/dllm/diffusiongemma.md

Co-authored-by: jgerh <163925524+jgerh@users.noreply.github.com>

* Update docs/guides/dllm/finetune.mdx

Co-authored-by: jgerh <163925524+jgerh@users.noreply.github.com>

* Update docs/guides/dllm/finetune.mdx

Co-authored-by: jgerh <163925524+jgerh@users.noreply.github.com>

* Update docs/guides/dllm/diffusiongemma.md

Co-authored-by: jgerh <163925524+jgerh@users.noreply.github.com>

* Update docs/guides/dllm/diffusiongemma.mdx

Co-authored-by: jgerh <163925524+jgerh@users.noreply.github.com>

* Update docs/guides/dllm/finetune.mdx

Co-authored-by: jgerh <163925524+jgerh@users.noreply.github.com>

* Update docs/guides/dllm/finetune.mdx

Co-authored-by: jgerh <163925524+jgerh@users.noreply.github.com>

* Update docs/guides/dllm/finetune.mdx

Co-authored-by: jgerh <163925524+jgerh@users.noreply.github.com>

* Update docs/guides/dllm/diffusiongemma.mdx

Co-authored-by: jgerh <163925524+jgerh@users.noreply.github.com>

* Update docs/guides/dllm/diffusiongemma.mdx

Co-authored-by: jgerh <163925524+jgerh@users.noreply.github.com>

* Update docs/guides/dllm/diffusiongemma.mdx

Co-authored-by: jgerh <163925524+jgerh@users.noreply.github.com>

* Update docs/guides/dllm/diffusiongemma.mdx

Co-authored-by: jgerh <163925524+jgerh@users.noreply.github.com>

* Update docs/guides/dllm/finetune.mdx

Co-authored-by: jgerh <163925524+jgerh@users.noreply.github.com>

* Update docs/guides/dllm/finetune.mdx

Co-authored-by: jgerh <163925524+jgerh@users.noreply.github.com>

* Update docs/guides/dllm/finetune.mdx

Co-authored-by: jgerh <163925524+jgerh@users.noreply.github.com>

* Update docs/guides/dllm/finetune.mdx

Co-authored-by: jgerh <163925524+jgerh@users.noreply.github.com>

* Update docs/guides/dllm/finetune.mdx

Co-authored-by: jgerh <163925524+jgerh@users.noreply.github.com>

* Update docs/guides/dllm/finetune.mdx

Co-authored-by: jgerh <163925524+jgerh@users.noreply.github.com>

* Update docs/guides/dllm/finetune.mdx

Co-authored-by: jgerh <163925524+jgerh@users.noreply.github.com>

* Update docs/guides/dllm/finetune.mdx

Co-authored-by: jgerh <163925524+jgerh@users.noreply.github.com>

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Signed-off-by: Kashif Rasul <kashif.rasul@gmail.com>
Co-authored-by: jgerh <163925524+jgerh@users.noreply.github.com>