Move conda installation from deprecated DEBs to Miniconda installer

[Copilot]

Conda's DEB packages are officially deprecated and the manual DEB download approach (introduced as a workaround for the APT SHA1 signature rejection) is not a supported installation method. This switches to the official Miniconda bash installer.

Changes

src/conda/install.sh

• Replaces the ~70-line manual DEB fetch/parse/install block with the official Miniconda3-latest-Linux-{arch}.sh installer run in batch mode (-b -p ${CONDA_DIR})
• Expands architecture support from x86_64-only to x86_64 + aarch64 via a case statement mapping to MINICONDA_ARCH
• For specific conda versions: installs latest Miniconda, then pins via conda install conda=VERSION with explicit error handling
• CONDA_SCRIPT now uses ${CONDA_DIR} variable consistently

# Before: parse Packages index, download .deb, apt-get install .deb (~70 lines)

# After:
MINICONDA_URL="https://repo.anaconda.com/miniconda/Miniconda3-latest-Linux-${MINICONDA_ARCH}.sh"
curl -fsSL --connect-timeout 10 --max-time 120 "${MINICONDA_URL}" -o "${MINICONDA_INSTALLER}"
bash "${MINICONDA_INSTALLER}" -b -p "${CONDA_DIR}"

# For specific versions:
"${CONDA_DIR}/bin/conda" install -y "conda=${VERSION}"

src/conda/devcontainer-feature.json

• Updates version proposals from 4.11.0/4.12.0 to 24.11.3/24.7.1

Tests

• scenarios.json: changes test version from 4.12.0 → latest (old versions are incompatible with modern Miniconda's bundled Python)
• install_conda.sh: removes the hard-coded version grep, retains conda-forge channel validation

Original prompt

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This section details on the original issue you should resolve

<issue_title>Move away from manual installation of deprecated Conda DEBs</issue_title>
<issue_description>We moved away from installing Conda via APT in #1576 because of the GPG key no longer being acceptable (SHA1, which APT disabled on Feb 1st 2026). We now download and install the DEBs manually, but this is not the supported approach. Conda have suggested moving away from DEBs to other installer forms, which we should explore: conda/conda#14826</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Move away from manual installation of deprecated Conda DEBs #1583

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